Basic concepts and nomenclatureEdit
Each record of a linked list is often called an 'element' or 'node'.
The field of each node that contains the address of the next node is usually called the 'next link' or 'next pointer'. The remaining fields are known as the 'data', 'information', 'value', 'cargo', or 'payload' fields.
The 'head' of a list is its first node. The 'tail' of a list may refer either to the rest of the list after the head, or to the last node in the list. In Lisp and some derived languages, the next node may be called the 'cdr' (pronounced could-er) of the list, while the payload of the head node may be called the 'car'.
Singly linked listEdit
Singly linked lists contain nodes which have a data field as well as 'next' field, which points to the next node in line of nodes. Operations that can be performed on singly linked lists include insertion, deletion and traversal.
A singly linked list whose nodes contain two fields: an integer value and a link to the next node
The following code demonstrates how to add a new node with data "value" to the end of a singly linked list:
node addNode(node head, int value) { node temp, p; // declare two nodes temp and p temp = createNode(); // assume createNode creates a new node with data = 0 and next pointing to NULL. temp->data = value; // add element's value to data part of node if (head == NULL) { head = temp; // when linked list is empty } else { p = head; // assign head to p while (p->next != NULL) { p = p->next; // traverse the list until p is the last node. The last node always points to NULL. } p->next = temp; // Point the previous last node to the new node created. } return head; }
Doubly linked listEdit
In a 'doubly linked list', each node contains, besides the next-node link, a second link field pointing to the 'previous' node in the sequence. The two links may be called 'forward('s') and 'backwards', or 'next' and 'prev'('previous').
A doubly linked list whose nodes contain three fields: an integer value, the link forward to the next node, and the link backward to the previous node
A technique known as XOR-linking allows a doubly linked list to be implemented using a single link field in each node. However, this technique requires the ability to do bit operations on addresses, and therefore may not be available in some high-level languages.
Many modern operating systems use doubly linked lists to maintain references to active processes, threads, and other dynamic objects.[2] A common strategy for rootkits to evade detection is to unlink themselves from these lists.[3]
Multiply linked listEdit
In a 'multiply linked list', each node contains two or more link fields, each field being used to connect the same set of data records in a different order of same set (e.g., by name, by department, by date of birth, etc.). While doubly linked lists can be seen as special cases of multiply linked list, the fact that the two and more orders are opposite to each other leads to simpler and more efficient algorithms, so they are usually treated as a separate case.
Circular linked listEdit
In the last node of a list, the link field often contains a null reference, a special value is used to indicate the lack of further nodes. A less common convention is to make it point to the first node of the list; in that case, the list is said to be 'circular' or 'circularly linked'; otherwise, it is said to be 'open' or 'linear'. It is a list where the last pointer points to the first node.
In the case of a circular doubly linked list, the first node also points to the last node of the list.
Sentinel nodesEdit
In some implementations an extra 'sentinel' or 'dummy' node may be added before the first data record or after the last one. This convention simplifies and accelerates some list-handling algorithms, by ensuring that all links can be safely dereferenced and that every list (even one that contains no data elements) always has a "first" and "last" node.
Empty listsEdit
An empty list is a list that contains no data records. This is usually the same as saying that it has zero nodes. If sentinel nodes are being used, the list is usually said to be empty when it has only sentinel nodes.
Hash linkingEdit
The link fields need not be physically part of the nodes. If the data records are stored in an array and referenced by their indices, the link field may be stored in a separate array with the same indices as the data records.
List handlesEdit
Since a reference to the first node gives access to the whole list, that reference is often called the 'address', 'pointer', or 'handle' of the list. Algorithms that manipulate linked lists usually get such handles to the input lists and return the handles to the resulting lists. In fact, in the context of such algorithms, the word "list" often means "list handle". In some situations, however, it may be convenient to refer to a list by a handle that consists of two links, pointing to its first and last nodes.
Combining alternativesEdit
The alternatives listed above may be arbitrarily combined in almost every way, so one may have circular doubly linked lists without sentinels, circular singly linked lists with sentinels, etc.
TradeoffsEdit
As with most choices in computer programming and design, no method is well suited to all circumstances. A linked list data structure might work well in one case, but cause problems in another. This is a list of some of the common tradeoffs involving linked list structures.
Linked lists vs. dynamic arraysEdit
A dynamic array is a data structure that allocates all elements contiguously in memory, and keeps a count of the current number of elements. If the space reserved for the dynamic array is exceeded, it is reallocated and (possibly) copied, which is an expensive operation.
Linked lists have several advantages over dynamic arrays. Insertion or deletion of an element at a specific point of a list, assuming that we have indexed a pointer to the node (before the one to be removed, or before the insertion point) already, is a constant-time operation (otherwise without this reference it is O(n)), whereas insertion in a dynamic array at random locations will require moving half of the elements on average, and all the elements in the worst case. While one can "delete" an element from an array in constant time by somehow marking its slot as "vacant", this causes fragmentation that impedes the performance of iteration.
Moreover, arbitrarily many elements may be inserted into a linked list, limited only by the total memory available; while a dynamic array will eventually fill up its underlying array data structure and will have to reallocate—an expensive operation, one that may not even be possible if memory is fragmented, although the cost of reallocation can be averaged over insertions, and the cost of an insertion due to reallocation would still be amortized O(1). This helps with appending elements at the array's end, but inserting into (or removing from) middle positions still carries prohibitive costs due to data moving to maintain contiguity. An array from which many elements are removed may also have to be resized in order to avoid wasting too much space.
On the other hand, dynamic arrays (as well as fixed-size array data structures) allow constant-time random access, while linked lists allow only sequential access to elements. Singly linked lists, in fact, can be easily traversed in only one direction. This makes linked lists unsuitable for applications where it's useful to look up an element by its index quickly, such as heapsort. Sequential access on arrays and dynamic arrays is also faster than on linked lists on many machines, because they have optimal locality of reference and thus make good use of data caching.
Another disadvantage of linked lists is the extra storage needed for references, which often makes them impractical for lists of small data items such as characters or boolean values, because the storage overhead for the links may exceed by a factor of two or more the size of the data. In contrast, a dynamic array requires only the space for the data itself (and a very small amount of control data).[note 1] It can also be slow, and with a naïve allocator, wasteful, to allocate memory separately for each new element, a problem generally solved using memory pools.
Some hybrid solutions try to combine the advantages of the two representations. Unrolled linked lists store several elements in each list node, increasing cache performance while decreasing memory overhead for references. CDR coding does both these as well, by replacing references with the actual data referenced, which extends off the end of the referencing record.
A good example that highlights the pros and cons of using dynamic arrays vs. linked lists is by implementing a program that resolves the Josephus problem. The Josephus problem is an election method that works by having a group of people stand in a circle. Starting at a predetermined person, one may count around the circle n times. Once the nth person is reached, one should remove them from the circle and have the members close the circle. The process is repeated until only one person is left. That person wins the election. This shows the strengths and weaknesses of a linked list vs. a dynamic array, because if the people are viewed as connected nodes in a circular linked list, then it shows how easily the linked list is able to delete nodes (as it only has to rearrange the links to the different nodes). However, the linked list will be poor at finding the next person to remove and will need to search through the list until it finds that person. A dynamic array, on the other hand, will be poor at deleting nodes (or elements) as it cannot remove one node without individually shifting all the elements up the list by one. However, it is exceptionally easy to find the nth person in the circle by directly referencing them by their position in the array.
The list ranking problem concerns the efficient conversion of a linked list representation into an array. Although trivial for a conventional computer, solving this problem by a parallel algorithm is complicated and has been the subject of much research.
A balanced tree has similar memory access patterns and space overhead to a linked list while permitting much more efficient indexing, taking O(log n) time instead of O(n) for a random access. However, insertion and deletion operations are more expensive due to the overhead of tree manipulations to maintain balance. Schemes exist for trees to automatically maintain themselves in a balanced state: AVL trees or red–black trees.
Singly linked linear lists vs. other listsEdit
While doubly linked and circular lists have advantages over singly linked linear lists, linear lists offer some advantages that make them preferable in some situations.
A singly linked linear list is a recursive data structure, because it contains a pointer to a smaller object of the same type. For that reason, many operations on singly linked linear lists (such as merging two lists, or enumerating the elements in reverse order) often have very simple recursive algorithms, much simpler than any solution using iterative commands. While those recursive solutions can be adapted for doubly linked and circularly linked lists, the procedures generally need extra arguments and more complicated base cases.
Linear singly linked lists also allow tail-sharing, the use of a common final portion of sub-list as the terminal portion of two different lists. In particular, if a new node is added at the beginning of a list, the former list remains available as the tail of the new one—a simple example of a persistent data structure. Again, this is not true with the other variants: a node may never belong to two different circular or doubly linked lists.
In particular, end-sentinel nodes can be shared among singly linked non-circular lists. The same end-sentinel node may be used for every such list. In Lisp, for example, every proper list ends with a link to a special node, denoted by nil or (), whose CAR and CDR links point to itself. Thus a Lisp procedure can safely take the CAR or CDR of any list.
The advantages of the fancy variants are often limited to the complexity of the algorithms, not in their efficiency. A circular list, in particular, can usually be emulated by a linear list together with two variables that point to the first and last nodes, at no extra cost.
Doubly linked vs. singly linkedEdit
Double-linked lists require more space per node (unless one uses XOR-linking), and their elementary operations are more expensive; but they are often easier to manipulate because they allow fast and easy sequential access to the list in both directions. In a doubly linked list, one can insert or delete a node in a constant number of operations given only that node's address. To do the same in a singly linked list, one must have the address of the pointer to that node, which is either the handle for the whole list (in case of the first node) or the link field in the previous node. Some algorithms require access in both directions. On the other hand, doubly linked lists do not allow tail-sharing and cannot be used as persistent data structures.
Circularly linked vs. linearly linkedEdit
A circularly linked list may be a natural option to represent arrays that are naturally circular, e.g. the corners of a polygon, a pool of buffers that are used and released in FIFO ("first in, first out") order, or a set of processes that should be time-shared in round-robin order. In these applications, a pointer to any node serves as a handle to the whole list.
With a circular list, a pointer to the last node gives easy access also to the first node, by following one link. Thus, in applications that require access to both ends of the list (e.g., in the implementation of a queue), a circular structure allows one to handle the structure by a single pointer, instead of two.
A circular list can be split into two circular lists, in constant time, by giving the addresses of the last node of each piece. The operation consists in swapping the contents of the link fields of those two nodes. Applying the same operation to any two nodes in two distinct lists joins the two list into one. This property greatly simplifies some algorithms and data structures, such as the quad-edge and face-edge.
The simplest representation for an empty circular list (when such a thing makes sense) is a null pointer, indicating that the list has no nodes. Without this choice, many algorithms have to test for this special case, and handle it separately. By contrast, the use of null to denote an empty linear list is more natural and often creates fewer special cases.
For some applications, it can be useful to use singly linked lists that can vary between being circular and being linear, or even circular with a linear initial segment. Algorithms for searching or otherwise operating on these have to take precautions to avoid accidentally entering an endless loop. One usual method is to have a second pointer walking the list at half or double the speed, and if both pointers meet at the same node, you know you found a cycle.
Using sentinel nodesEdit
Sentinel node may simplify certain list operations, by ensuring that the next or previous nodes exist for every element, and that even empty lists have at least one node. One may also use a sentinel node at the end of the list, with an appropriate data field, to eliminate some end-of-list tests. For example, when scanning the list looking for a node with a given value x, setting the sentinel's data field to x makes it unnecessary to test for end-of-list inside the loop. Another example is the merging two sorted lists: if their sentinels have data fields set to +∞, the choice of the next output node does not need special handling for empty lists.
However, sentinel nodes use up extra space (especially in applications that use many short lists), and they may complicate other operations (such as the creation of a new empty list).
However, if the circular list is used merely to simulate a linear list, one may avoid some of this complexity by adding a single sentinel node to every list, between the last and the first data nodes. With this convention, an empty list consists of the sentinel node alone, pointing to itself via the next-node link. The list handle should then be a pointer to the last data node, before the sentinel, if the list is not empty; or to the sentinel itself, if the list is empty.
The same trick can be used to simplify the handling of a doubly linked linear list, by turning it into a circular doubly linked list with a single sentinel node. However, in this case, the handle should be a single pointer to the dummy node itself.[8]
Types of Linked List
A linked list is a linear data structure, in which the elements are not stored at contiguous memory locations. The elements in a linked list are linked using pointers. In simple words, a linked list consists of nodes where each node contains a data field and a reference(link) to the next node in the list.
Types Of Linked List
- Singly Linked List: It is the simplest type of linked list in which every node contains some data and a pointer to the next node of the same data type. The node contains a pointer to the next node means that the node stores the address of the next node in the sequence. A single linked list allows traversal of data only in one way. Below is the image for the same:
- Structure of Singly Linked List:
C++
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// Node of a doubly linked list class Node { public: int data; // Pointer to next node in LL Node* next; }; |
Java
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// Node of a doubly linked list static class Node { int data;
// Pointer to next node in LL Node next; }; //this code is contributed by shivani |
Python3
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# structure of Node class Node: def __init__(self, data): self.data = data self.next = None |
C#
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// Structure of Node public class Node { public int data;
// Pointer to next node in LL public Node next; }; //this code is contributed by shivanisinghss2110 |
Javascript
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// Node of a doubly linked list class Node { constructor() { this.data=0;
// Pointer to next node this.next=null; } } // This code is contributed by SHUBHAMSINGH10 |
- Creation and Traversal of Singly Linked List:
C++
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// C++ program to illustrate creation // and traversal of Singly Linked List #include <bits/stdc++.h> using namespace std; // Structure of Node class Node { public: int data; Node* next; }; // Function to print the content of // linked list starting from the // given node void printList(Node* n) { // Iterate till n reaches NULL while (n != NULL) { // Print the data cout << n->data << " "; n = n->next; } } // Driver Code int main() { Node* head = NULL; Node* second = NULL; Node* third = NULL; // Allocate 3 nodes in the heap head = new Node(); second = new Node(); third = new Node(); // Assign data in first node head->data = 1; // Link first node with second head->next = second; // Assign data to second node second->data = 2; second->next = third; // Assign data to third node third->data = 3; third->next = NULL; printList(head); return 0; } |
Java
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// Java program to illustrate // creation and traversal of // Singly Linked List class GFG{ // Structure of Node static class Node { int data; Node next; }; // Function to print the content of // linked list starting from the // given node static void printList(Node n) { // Iterate till n reaches null while (n != null) { // Print the data System.out.print(n.data + " "); n = n.next; } } // Driver Code public static void main(String[] args) { Node head = null; Node second = null; Node third = null; // Allocate 3 nodes in // the heap head = new Node(); second = new Node(); third = new Node(); // Assign data in first // node head.data = 1; // Link first node with // second head.next = second; // Assign data to second // node second.data = 2; second.next = third; // Assign data to third // node third.data = 3; third.next = null; printList(head); } } // This code is contributed by Princi Singh |
C#
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// C# program to illustrate // creation and traversal of // Singly Linked List using System; class GFG{ // Structure of Node public class Node { public int data; public Node next; }; // Function to print the content of // linked list starting from the // given node static void printList(Node n) {
// Iterate till n reaches null while (n != null) {
// Print the data Console.Write(n.data + " "); n = n.next; } } // Driver Code public static void Main(String[] args) { Node head = null; Node second = null; Node third = null;
// Allocate 3 nodes in // the heap head = new Node(); second = new Node(); third = new Node();
// Assign data in first // node head.data = 1;
// Link first node with // second head.next = second;
// Assign data to second // node second.data = 2; second.next = third;
// Assign data to third // node third.data = 3; third.next = null;
printList(head); } } // This code is contributed by Amit Katiyar |
Python3
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# structure of Node class Node: def __init__(self, data): self.data = data self.next = None class LinkedList: def __init__(self): self.head = None self.last_node = None
# function to add elements to linked list def append(self, data): # if linked list is empty then last_node will be none so in if condition head will be created if self.last_node is None: self.head = Node(data) self.last_node = self.head # adding node to the tail of linked list else: self.last_node.next = Node(data) self.last_node = self.last_node.next
# function to print the content of linked list def display(self): current = self.head # traversing the linked list while current is not None: # at each node printing its data print(current.data, end=' ') # giving current next node current = current.next print() if __name__ == '__main__': L = LinkedList() # adding elements to the linked list L.append(1) L.append(2) L.append(3) L.append(4) # displaying elements of linked list L.display() |
Javascript
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<script> // JavaScript program to illustrate // creation and traversal of // Singly Linked List // Structure of Node class Node { constructor() { this.data=0; this.next=null; } } // Function to print the content of // linked list starting from the // given node function printList(n) { // Iterate till n reaches null while (n != null) { // Print the data document.write(n.data + " "); n = n.next; } } // Driver Code let head = null; let second = null; let third = null; // Allocate 3 nodes in // the heap head = new Node(); second = new Node(); third = new Node(); // Assign data in first // node head.data = 1; // Link first node with // second head.next = second; // Assign data to second // node second.data = 2; second.next = third; // Assign data to third // node third.data = 3; third.next = null; printList(head); // This code is contributed by unknown2108 </script> |
Output 1 2 3
- Doubly Linked List: A doubly linked list or a two-way linked list is a more complex type of linked list which contains a pointer to the next as well as the previous node in sequence, Therefore, it contains three parts are data, a pointer to the next node, and a pointer to the previous node. This would enable us to traverse the list in the backward direction as well. Below is the image for the same:
- Structure of Doubly Linked List:
C++
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// Node of a doubly linked list struct Node { int data; // Pointer to next node in DLL struct Node* next; // Pointer to the previous node in DLL struct Node* prev; }; |
Java
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// Doubly linked list // node static class Node { int data;
// Pointer to next node in DLL Node next;
// Pointer to the previous node in DLL Node prev; }; // This code is contributed by shivani |
Python3
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# structure of Node class Node: def __init__(self, data): self.previous = None self.data = data self.next = None |
C#
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// Doubly linked list // node public class Node { public int data;
// Pointer to next node in DLL public Node next;
// Pointer to the previous node in DLL public Node prev; }; // This code is contributed by shivanisinghss2110 |
- Creation and Traversal of Doubly Linked List:
C++
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// C++ program to illustrate creation // and traversal of Doubly Linked List #include <bits/stdc++.h> using namespace std; // Doubly linked list node class Node { public: int data; Node* next; Node* prev; }; // Function to push a new element in // the Doubly Linked List void push(Node** head_ref, int new_data) { // Allocate node Node* new_node = new Node(); // Put in the data new_node->data = new_data; // Make next of new node as // head and previous as NULL new_node->next = (*head_ref); new_node->prev = NULL; // Change prev of head node to // the new node if ((*head_ref) != NULL) (*head_ref)->prev = new_node; // Move the head to point to // the new node (*head_ref) = new_node; } // Function to traverse the Doubly LL // in the forward & backward direction void printList(Node* node) { Node* last; cout << "\nTraversal in forward" << " direction \n"; while (node != NULL) { // Print the data cout << " " << node->data << " "; last = node; node = node->next; } cout << "\nTraversal in reverse" << " direction \n"; while (last != NULL) { // Print the data cout << " " << last->data << " "; last = last->prev; } } // Driver Code int main() { // Start with the empty list Node* head = NULL; // Insert 6. // So linked list becomes 6->NULL push(&head, 6); // Insert 7 at the beginning. So // linked list becomes 7->6->NULL push(&head, 7); // Insert 1 at the beginning. So // linked list becomes 1->7->6->NULL push(&head, 1); cout << "Created DLL is: "; printList(head); return 0; } |
Java
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// Java program to illustrate // creation and traversal of // Doubly Linked List import java.util.*; class GFG{ // Doubly linked list // node static class Node { int data; Node next; Node prev; };
static Node head_ref;
// Function to push a new // element in the Doubly // Linked List static void push(int new_data) { // Allocate node Node new_node = new Node(); // Put in the data new_node.data = new_data; // Make next of new node as // head and previous as null new_node.next = head_ref; new_node.prev = null; // Change prev of head node to // the new node if (head_ref != null) head_ref.prev = new_node; // Move the head to point to // the new node head_ref = new_node; } // Function to traverse the // Doubly LL in the forward // & backward direction static void printList(Node node) { Node last = null; System.out.print("\nTraversal in forward" + " direction \n"); while (node != null) { // Print the data System.out.print(" " + node.data + " "); last = node; node = node.next; } System.out.print("\nTraversal in reverse" + " direction \n");
while (last != null) { // Print the data System.out.print(" " + last.data + " "); last = last.prev; } } // Driver Code public static void main(String[] args) { // Start with the empty list head_ref = null; // Insert 6. // So linked list becomes // 6.null push(6); // Insert 7 at the beginning. // So linked list becomes // 7.6.null push(7); // Insert 1 at the beginning. // So linked list becomes // 1.7.6.null push(1); System.out.print("Created DLL is: "); printList(head_ref); } } // This code is contributed by Princi Singh |
Python3
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# structure of Node class Node: def __init__(self, data): self.previous = None self.data = data self.next = None class DoublyLinkedList: def __init__(self): self.head = None self.start_node = None self.last_node = None # function to add elements to doubly linked list def append(self, data): # is doubly linked list is empty then last_node will be none so in if condition head will be created if self.last_node is None: self.head = Node(data) self.last_node = self.head # adding node to the tail of doubly linked list else: new_node = Node(data) self.last_node.next = new_node new_node.previous = self.last_node new_node.next = None self.last_node = new_node # function to printing and traversing the content of doubly linked list from left to right and right to left def display(self, Type): if Type == 'Left_To_Right': current = self.head while current is not None: print(current.data, end=' ') current = current.next print() else: current = self.last_node while current is not None: print(current.data, end=' ') current = current.previous print() if __name__ == '__main__': L = DoublyLinkedList() L.append(1) L.append(2) L.append(3) L.append(4) L.display('Left_To_Right') L.display('Right_To_Left') |
C#
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// C# program to illustrate // creation and traversal of // Doubly Linked List using System; class GFG{ // Doubly linked list // node public class Node { public int data; public Node next; public Node prev; };
static Node head_ref;
// Function to push a new // element in the Doubly // Linked List static void push(int new_data) {
// Allocate node Node new_node = new Node(); // Put in the data new_node.data = new_data; // Make next of new node as // head and previous as null new_node.next = head_ref; new_node.prev = null; // Change prev of head node to // the new node if (head_ref != null) head_ref.prev = new_node; // Move the head to point to // the new node head_ref = new_node; } // Function to traverse the // Doubly LL in the forward // & backward direction static void printList(Node node) { Node last = null; Console.Write("\nTraversal in forward" + " direction \n");
while (node != null) {
// Print the data Console.Write(" " + node.data + " "); last = node; node = node.next; } Console.Write("\nTraversal in reverse" + " direction \n");
while (last != null) {
// Print the data Console.Write(" " + last.data + " "); last = last.prev; } } // Driver Code public static void Main(String[] args) {
// Start with the empty list head_ref = null; // Insert 6. // So linked list becomes // 6.null push(6); // Insert 7 at the beginning. // So linked list becomes // 7.6.null push(7); // Insert 1 at the beginning. // So linked list becomes // 1.7.6.null push(1); Console.Write("Created DLL is: "); printList(head_ref); } } // This code is contributed by Amit Katiyar |
Output Created DLL is: Traversal in forward direction 1 7 6 Traversal in reverse direction 6 7 1
- Circular Linked List: A circular linked list is that in which the last node contains the pointer to the first node of the list. While traversing a circular liked list, we can begin at any node and traverse the list in any direction forward and backward until we reach the same node we started. Thus, a circular linked list has no beginning and no end. Below is the image for the same:
- Structure of Circular Linked List:
C++
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// Structure for a node class Node { public: int data; // Pointer to next node in CLL Node* next; }; |
Java
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// Structure for a node static class Node { int data;
// Pointer to next node in CLL Node next; }; // This code is contributed by shivanisinghss2110 |
Python3
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# structure of Node class Node: def __init__(self, data): self.data = data self.next = None |
C#
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// Structure for a node public class Node { public int data;
// Pointer to next node in CLL public Node next; }; // This code is contributed by shivanisinghss2110 |
- Creation and Traversal of Circular Linked List:
C++
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// C++ program to illustrate creation // and traversal of Circular LL #include <bits/stdc++.h> using namespace std; // Structure for a node class Node { public: int data; Node* next; }; // Function to insert a node at the // beginning of Circular LL void push(Node** head_ref, int data) { Node* ptr1 = new Node(); Node* temp = *head_ref; ptr1->data = data; ptr1->next = *head_ref; // If linked list is not NULL then // set the next of last node if (*head_ref != NULL) { while (temp->next != *head_ref) { temp = temp->next; } temp->next = ptr1; } // For the first node else ptr1->next = ptr1; *head_ref = ptr1; } // Function to print nodes in the // Circular Linked List void printList(Node* head) { Node* temp = head; if (head != NULL) { do { // Print the data cout << temp->data << " "; temp = temp->next; } while (temp != head); } } // Driver Code int main() { // Initialize list as empty Node* head = NULL; // Created linked list will // be 11->2->56->12 push(&head, 12); push(&head, 56); push(&head, 2); push(&head, 11); cout << "Contents of Circular" << " Linked List\n "; printList(head); return 0; } |
Java
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// Java program to illustrate // creation and traversal of // Circular LL import java.util.*; class GFG{ // Structure for a // node static class Node { int data; Node next; }; // Function to insert a node // at the beginning of Circular // LL static Node push(Node head_ref, int data) { Node ptr1 = new Node(); Node temp = head_ref; ptr1.data = data; ptr1.next = head_ref; // If linked list is not // null then set the next // of last node if (head_ref != null) { while (temp.next != head_ref) { temp = temp.next; } temp.next = ptr1; } // For the first node else ptr1.next = ptr1; head_ref = ptr1; return head_ref; } // Function to print nodes in // the Circular Linked List static void printList(Node head) { Node temp = head; if (head != null) { do { // Print the data System.out.print(temp.data + " "); temp = temp.next; } while (temp != head); } } // Driver Code public static void main(String[] args) { // Initialize list as empty Node head = null; // Created linked list will // be 11.2.56.12 head = push(head, 12); head = push(head, 56); head = push(head, 2); head = push(head, 11); System.out.print("Contents of Circular" + " Linked List\n "); printList(head); } } // This code is contributed by gauravrajput1 |
Python3
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# structure of Node class Node: def __init__(self, data): self.data = data self.next = None class CircularLinkedList: def __init__(self): self.head = None self.last_node = None # function to add elements to circular linked list def append(self, data): # is circular linked list is empty then last_node will be none so in if condition head will be created if self.last_node is None: self.head = Node(data) self.last_node = self.head # adding node to the tail of circular linked list else: self.last_node.next = Node(data) self.last_node = self.last_node.next self.last_node.next = self.head # function to print the content of circular linked list def display(self): current = self.head while current is not None: print(current.data, end=' ') current = current.next if current == self.head: break print() if __name__ == '__main__': L = CircularLinkedList() L.append(1) L.append(2) L.append(3) L.append(4) L.display() |
C#
|
// C# program to illustrate // creation and traversal of // Circular LL using System; class GFG{ // Structure for a // node public class Node { public int data; public Node next; }; // Function to insert a node // at the beginning of Circular // LL static Node push(Node head_ref, int data) { Node ptr1 = new Node(); Node temp = head_ref; ptr1.data = data; ptr1.next = head_ref;
// If linked list is not // null then set the next // of last node if (head_ref != null) { while (temp.next != head_ref) { temp = temp.next; } temp.next = ptr1; } // For the first node else ptr1.next = ptr1; head_ref = ptr1; return head_ref; } // Function to print nodes in // the Circular Linked List static void printList(Node head) { Node temp = head;
if (head != null) { do {
// Print the data Console.Write(temp.data + " "); temp = temp.next; } while (temp != head); } } // Driver Code public static void Main(String[] args) {
// Initialize list as empty Node head = null;
// Created linked list will // be 11.2.56.12 head = push(head, 12); head = push(head, 56); head = push(head, 2); head = push(head, 11); Console.Write("Contents of Circular " + "Linked List\n ");
printList(head); } } // This code is contributed by gauravrajput1 |
Output Contents of Circular Linked List 11 2 56 12
- Doubly Circular linked list: A Doubly Circular linked list or a circular two-way linked list is a more complex type of linked-list that contains a pointer to the next as well as the previous node in the sequence. The difference between the doubly linked and circular doubly list is the same as that between a singly linked list and a circular linked list. The circular doubly linked list does not contain null in the previous field of the first node. Below is the image for the same:
- Structure of Doubly Circular Linked List:
C++
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// Node of doubly circular linked list struct Node { int data; // Pointer to next node in DCLL struct Node* next; // Pointer to the previous node in DCLL struct Node* prev; }; |
Java
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// Structure of a Node static class Node { int data;
// Pointer to next node in DCLL Node next;
// Pointer to the previous node in DCLL Node prev; }; //this code is contributed by shivanisinghss2110 |
Python3
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# structure of Node class Node: def __init__(self, data): self.previous = None self.data = data self.next = None |
C#
|
// Structure of a Node public class Node { public int data;
// Pointer to next node in DCLL public Node next;
// Pointer to the previous node in DCLL public Node prev; }; // This code is contributed by shivanisinghss2110 |
- Creation and Traversal of Doubly Circular Linked List:
C++
|
// C++ program to illustrate creation // & traversal of Doubly Circular LL #include <bits/stdc++.h> using namespace std; // Structure of a Node struct Node { int data; struct Node* next; struct Node* prev; }; // Function to insert Node at // the beginning of the List void insertBegin(struct Node** start, int value) { // If the list is empty if (*start == NULL) { struct Node* new_node = new Node; new_node->data = value; new_node->next = new_node->prev = new_node; *start = new_node; return; } // Pointer points to last Node struct Node* last = (*start)->prev; struct Node* new_node = new Node; // Inserting the data new_node->data = value; // Update the previous and // next of new node new_node->next = *start; new_node->prev = last; // Update next and previous // pointers of start & last last->next = (*start)->prev = new_node; // Update start pointer *start = new_node; } // Function to traverse the circular // doubly linked list void display(struct Node* start) { struct Node* temp = start; printf("\nTraversal in" " forward direction \n"); while (temp->next != start) { printf("%d ", temp->data); temp = temp->next; } printf("%d ", temp->data); printf("\nTraversal in " "reverse direction \n"); Node* last = start->prev; temp = last; while (temp->prev != last) { // Print the data printf("%d ", temp->data); temp = temp->prev; } printf("%d ", temp->data); } // Driver Code int main() { // Start with the empty list struct Node* start = NULL; // Insert 5 // So linked list becomes 5->NULL insertBegin(&start, 5); // Insert 4 at the beginning // So linked list becomes 4->5 insertBegin(&start, 4); // Insert 7 at the end // So linked list becomes 7->4->5 insertBegin(&start, 7); printf("Created circular doubly" " linked list is: "); display(start); return 0; } |
Java
|
// Java program to illustrate creation // & traversal of Doubly Circular LL import java.util.*; class GFG{ // Structure of a Node static class Node { int data; Node next; Node prev; };
// Start with the empty list static Node start = null; // Function to insert Node at // the beginning of the List static void insertBegin( int value) { // If the list is empty if (start == null) { Node new_node = new Node(); new_node.data = value; new_node.next = new_node.prev = new_node; start = new_node; return; } // Pointer points to last Node Node last = (start).prev; Node new_node = new Node(); // Inserting the data new_node.data = value; // Update the previous and // next of new node new_node.next = start; new_node.prev = last; // Update next and previous // pointers of start & last last.next = (start).prev = new_node; // Update start pointer start = new_node; } // Function to traverse the circular // doubly linked list static void display() { Node temp = start; System.out.printf("\nTraversal in" +" forward direction \n"); while (temp.next != start) { System.out.printf("%d ", temp.data); temp = temp.next; } System.out.printf("%d ", temp.data); System.out.printf("\nTraversal in " + "reverse direction \n"); Node last = start.prev; temp = last; while (temp.prev != last) { // Print the data System.out.printf("%d ", temp.data); temp = temp.prev; } System.out.printf("%d ", temp.data); } // Driver Code public static void main(String[] args) { // Insert 5 // So linked list becomes 5.null insertBegin( 5); // Insert 4 at the beginning // So linked list becomes 4.5 insertBegin( 4); // Insert 7 at the end // So linked list becomes 7.4.5 insertBegin( 7); System.out.printf("Created circular doubly" + " linked list is: "); display(); } } // This code is contributed by shikhasingrajput |
Python3
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# structure of Node class Node: def __init__(self, data): self.previous = None self.data = data self.next = None class DoublyLinkedList: def __init__(self): self.head = None self.start_node = None self.last_node = None # function to add elements to doubly linked list def append(self, data): # is doubly linked list is empty then last_node will be none so in if condition head will be created if self.last_node is None: self.head = Node(data) self.last_node = self.head # adding node to the tail of doubly linked list else: new_node = Node(data) self.last_node.next = new_node new_node.previous = self.last_node new_node.next = self.head self.last_node = new_node # function to print the content of doubly linked list def display(self, Type = 'Left_To_Right'): if Type == 'Left_To_Right': current = self.head while current.next is not None: print(current.data, end=' ') current = current.next if current == self.head: break print() else: current = self.last_node while current.previous is not None: print(current.data, end=' ') current = current.previous if current == self.last_node.next: print(self.last_node.next.data, end=' ') break print() if __name__ == '__main__': L = DoublyLinkedList() L.append(1) L.append(2) L.append(3) L.append(4) L.display('Left_To_Right') L.display('Right_To_Left') |
C#
|
// C# program to illustrate creation // & traversal of Doubly Circular LL using System; public class GFG{ // Structure of a Node public class Node { public int data; public Node next; public Node prev; };
// Start with the empty list static Node start = null; // Function to insert Node at // the beginning of the List static void insertBegin( int value) { Node new_node = new Node();
// If the list is empty if (start == null) {
new_node.data = value; new_node.next = new_node.prev = new_node; start = new_node; return; } // Pointer points to last Node Node last = (start).prev; // Inserting the data new_node.data = value; // Update the previous and // next of new node new_node.next = start; new_node.prev = last; // Update next and previous // pointers of start & last last.next = (start).prev = new_node; // Update start pointer start = new_node; } // Function to traverse the circular // doubly linked list static void display() { Node temp = start; Console.Write("\nTraversal in" +" forward direction \n"); while (temp.next != start) { Console.Write(temp.data + " "); temp = temp.next; } Console.Write(temp.data + " "); Console.Write("\nTraversal in " + "reverse direction \n"); Node last = start.prev; temp = last; while (temp.prev != last) { // Print the data Console.Write( temp.data + " "); temp = temp.prev; } Console.Write( temp.data + " "); } // Driver Code public static void Main(String[] args) { // Insert 5 // So linked list becomes 5.null insertBegin( 5); // Insert 4 at the beginning // So linked list becomes 4.5 insertBegin( 4); // Insert 7 at the end // So linked list becomes 7.4.5 insertBegin( 7); Console.Write("Created circular doubly" + " linked list is: "); display(); } } // This code is contributed by 29AjayKumar |
Output Created circular doubly linked list is: Traversal in forward direction 7 4 5 Traversal in reverse direction 5 4 7
- Header Linked List: A header linked list is a special type of linked list which contains a header node at the beginning of the list. So, in a header linked list START will not point to the first node of the list but START will contain the address of the header node. Below is the image for Grounded Header Linked List:
- Structure of Grounded Header Linked List:
C++
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// Structure of the list struct link { int info; // Pointer to the next node struct link* next; }; |
Python3
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# structure of Node class Node: def __init__(self, data): self.data = data self.next = None |
Java
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// Structure of the list static class link { int info;
// Pointer to the next node link next; }; // this code is contributed by shivanisinghss2110 |
C#
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// Structure of the list public class link { public int info;
// Pointer to the next node public link next; }; // this code is contributed by shivanisinghss2110 |
- Creation and Traversal of Header Linked List:
C++
|
// C++ program to illustrate creation // and traversal of Header Linked List #include <bits/stdc++.h> // #include <malloc.h> // #include <stdio.h> // Structure of the list struct link { int info; struct link* next; }; // Empty List struct link* start = NULL; // Function to create header of the // header linked list struct link* create_header_list(int data) { // Create a new node struct link *new_node, *node; new_node = (struct link*) malloc(sizeof(struct link)); new_node->info = data; new_node->next = NULL; // If it is the first node if (start == NULL) { // Initialize the start start = (struct link*) malloc(sizeof(struct link)); start->next = new_node; } else { // Insert the node in the end node = start; while (node->next != NULL) { node = node->next; } node->next = new_node; } return start; } // Function to display the // header linked list struct link* display() { struct link* node; node = start; node = node->next; // Traverse until node is // not NULL while (node != NULL) { // Print the data printf("%d ", node->info); node = node->next; } printf("\n"); // Return the start pointer return start; } // Driver Code int main() { // Create the list create_header_list(11); create_header_list(12); create_header_list(13); // Print the list printf("List After inserting" " 3 elements:\n"); display(); create_header_list(14); create_header_list(15); // Print the list printf("List After inserting" " 2 more elements:\n"); display(); return 0; } |
Java
|
// Java program to illustrate creation // and traversal of Header Linked List class GFG{ // Structure of the list static class link { int info; link next; }; // Empty List static link start = null; // Function to create header of the // header linked list static link create_header_list(int data) { // Create a new node link new_node, node; new_node = new link(); new_node.info = data; new_node.next = null; // If it is the first node if (start == null) { // Initialize the start start = new link(); start.next = new_node; } else { // Insert the node in the end node = start; while (node.next != null) { node = node.next; } node.next = new_node; } return start; } // Function to display the // header linked list static link display() { link node; node = start; node = node.next; // Traverse until node is // not null while (node != null) { // Print the data System.out.printf("%d ", node.info); node = node.next; } System.out.printf("\n"); // Return the start pointer return start; } // Driver Code public static void main(String[] args) { // Create the list create_header_list(11); create_header_list(12); create_header_list(13); // Print the list System.out.printf("List After inserting" + " 3 elements:\n"); display(); create_header_list(14); create_header_list(15); // Print the list System.out.printf("List After inserting" + " 2 more elements:\n"); display(); } } // This code is contributed by 29AjayKumar |
Python3
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# structure of Node class Node: def __init__(self, data): self.data = data self.next = None class LinkedList: def __init__(self): self.head = Node(0) self.last_node = self.head # function to add elements to header linked list def append(self, data): self.last_node.next = Node(data) self.last_node = self.last_node.next # function to print the content of header linked list def display(self): current = self.head.next # traversing the header linked list while current is not None: # at each node printing its data print(current.data, end=' ') # giving current next node current = current.next # print(self.head.data) print() if __name__ == '__main__': L = LinkedList() # adding elements to the header linked list L.append(1) L.append(2) L.append(3) L.append(4) # displaying elements of header linked list L.display() |
C#
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// C# program to illustrate creation // and traversal of Header Linked List using System; public class GFG{ // Structure of the list public class link { public int info; public link next; }; // Empty List static link start = null; // Function to create header of the // header linked list static link create_header_list(int data) { // Create a new node link new_node, node; new_node = new link(); new_node.info = data; new_node.next = null; // If it is the first node if (start == null) { // Initialize the start start = new link(); start.next = new_node; } else { // Insert the node in the end node = start; while (node.next != null) { node = node.next; } node.next = new_node; } return start; } // Function to display the // header linked list static link display() { link node; node = start; node = node.next; // Traverse until node is // not null while (node != null) { // Print the data Console.Write("{0} ", node.info); node = node.next; } Console.Write("\n"); // Return the start pointer return start; } // Driver Code public static void Main(String[] args) { // Create the list create_header_list(11); create_header_list(12); create_header_list(13); // Print the list Console.Write("List After inserting" + " 3 elements:\n"); display(); create_header_list(14); create_header_list(15); // Print the list Console.Write("List After inserting" + " 2 more elements:\n"); display(); } }
// This code is contributed by 29AjayKumar |
Output List After inserting 3 elements: 11 12 13 List After inserting 2 more elements: 11 12 13 14 15
Article Tags :
Data Structures
Linked List
circular linked list
doubly linked list
Linked Lists
Practice Tags :
Data Structures
Linked List
circular linked list
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Linked List Data Structure
- Last Updated : 01 Feb, 2022
Practice Problems on Linked List
Recent Articles on Linked List
A linked list is a linear data structure, in which the elements are not stored at contiguous memory locations. The elements in a linked list are linked using pointers as shown in the below image:
In simple words, a linked list consists of nodes where each node contains a data field and a reference(link) to the next node in the list.
Topics :
- Singly Linked List
- Circular Linked List
- Doubly Linked List
- Misc
- Quick Links
Singly Linked List :
- Introduction to Linked List
- Linked List vs Array
- Linked List Insertion
- Linked List Deletion (Deleting a given key)
- Linked List Deletion (Deleting a key at given position)
- Write a function to delete a Linked List
- Find Length of a Linked List (Iterative and Recursive)
- Search an element in a Linked List (Iterative and Recursive)
- Write a function to get Nth node in a Linked List
- Nth node from the end of a Linked List
- Print the middle of a given linked list
- Write a function that counts the number of times a given int occurs in a Linked List
- Detect loop in a linked list
- Find length of loop in linked list
- Function to check if a singly linked list is palindrome
- Remove duplicates from a sorted linked list
- Remove duplicates from an unsorted linked list
- Swap nodes in a linked list without swapping data
- Pairwise swap elements of a given linked list
- Move last element to front of a given Linked List
- Intersection of two Sorted Linked Lists
- Intersection point of two Linked Lists.
- QuickSort on Singly Linked List
- Segregate even and odd nodes in a Linked List
- Reverse a linked list
More >>
Circular Linked List :
- Circular Linked List Introduction and Applications,
- Circular Linked List Traversal
- Split a Circular Linked List into two halves
- Sorted insert for circular linked list
- Check if a linked list is Circular Linked List
- Convert a Binary Tree to a Circular Doubly Link List
- Circular Singly Linked List | Insertion
- Deletion from a Circular Linked List
- Circular Queue | Set 2 (Circular Linked List Implementation)
- Count nodes in Circular linked list
- Josephus Circle using circular linked list
- Convert singly linked list into circular linked list
- Circular Linked List | Set 1 (Introduction and Applications)
- Circular Linked List | Set 2 (Traversal)
- Implementation of Deque using circular array
- Exchange first and last nodes in Circular Linked List
More >>
Doubly Linked List :
- Doubly Linked List Introduction and Insertion
- Delete a node in a Doubly Linked List
- Reverse a Doubly Linked List
- The Great Tree-List Recursion Problem.
- Copy a linked list with next and arbit pointer
- QuickSort on Doubly Linked List
- Swap Kth node from beginning with Kth node from end in a Linked List
- Merge Sort for Doubly Linked List
- Create a Doubly Linked List from a Ternary Tree
- Find pairs with given sum in doubly linked list
- Insert value in sorted way in a sorted doubly linked list
- Delete a Doubly Linked List node at a given position
- Count triplets in a sorted doubly linked list whose sum is equal to a given value x
- Remove duplicates from a sorted doubly linked list
- Delete all occurrences of a given key in a doubly linked list
- Remove duplicates from an unsorted doubly linked list
- Sort the biotonic doubly linked list
- Sort a k sorted doubly linked list
- Convert a given Binary Tree to Doubly Linked List | Set
- Program to find size of Doubly Linked List
- Sorted insert in a doubly linked list with head and tail pointers
- Large number arithmetic using doubly linked list
- Rotate Doubly linked list by N nodes
- Priority Queue using doubly linked list
- Reverse a doubly linked list in groups of given size
- Doubly Circular Linked List | Set 1 (Introduction and Insertion)
- Doubly Circular Linked List | Set 2 (Deletion)
More >>
Misc :
- Skip List | Set 1 (Introduction)
- Skip List | Set 2 (Insertion)
- Skip List | Set 3 (Searching and Deletion)
- Reverse a stack without using extra space in O(n)
- An interesting method to print reverse of a linked list
- Linked List representation of Disjoint Set Data Structures
- Sublist Search (Search a linked list in another list)
- How to insert elements in C++ STL List ?
- Unrolled Linked List | Set 1 (Introduction)
- A Programmer’s approach of looking at Array vs. Linked List
- How to write C functions that modify head pointer of a Linked List?
- Given a linked list which is sorted, how will you insert in sorted way
- Can we reverse a linked list in less than O(n)?
- Practice questions for Linked List and Recursion
- Construct a Maximum Sum Linked List out of two Sorted Linked Lists having some Common nodes
- Given only a pointer to a node to be deleted in a singly linked list, how do you delete it?
- Why Quick Sort preferred for Arrays and Merge Sort for Linked Lists?
- Squareroot(n)-th node in a Linked List
- Find the fractional (or n/k – th) node in linked list
- Find modular node in a linked list
- Construct a linked list from 2D matrix
- Find smallest and largest elements in singly linked list
- Arrange consonants and vowels nodes in a linked list
- Partitioning a linked list around a given value and If we don’t care about making the elements of the list “stable”
- Modify contents of Linked List
Quick Links :
- ‘Practice Problems’ on Linked List
- ‘Videos’ on Linked List
- ‘Quizzes’ on Linked List
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Data Structure and Algorithms - Linked List
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A linked list is a sequence of data structures, which are connected together via links.
Linked List is a sequence of links which contains items. Each link contains a connection to another link. Linked list is the second most-used data structure after array. Following are the important terms to understand the concept of Linked List.
Link − Each link of a linked list can store a data called an element.
Next − Each link of a linked list contains a link to the next link called Next.
LinkedList − A Linked List contains the connection link to the first link called First.
Types
Singly Linked List
Singly linked lists contain nodes which have a data field as well as a next field, which points to the next node in the sequence. Operations that can be performed on singly linked lists are insertion, deletion and traversal.
head | | +-----+--+ +-----+--+ +-----+------+ | 1 |o-----> | 2 |o-----> | 3 | NULL | +-----+--+ +-----+--+ +-----+------+Internal implementation of CPython, the frames and evaluated variables are kept on a stack.
For this we need to iterate only forward aur get the head, therefore singly linked-list is used.
Doubly Linked List
Doubly linked lists contain node which have data field, next field and another link field prev pointing to the previous node in the sequence.
head | | +------+-----+--+ +--+-----+--+ +-----+------+ | | |o------> | |o------> | | | | NULL | 1 | | 2 | | 3 | NULL | | | | <------o| | <------o| | | +------+-----+--+ +--+-----+--+ +-----+------+The browser cache which allows you to hit the BACK and FORWARD button. Here we need to maintain a doubly linked list, with URLs as data field, to allow access in both direction. To go to previous URL we will use prev field and to go to next page we will use next field.
Circular Linked List
Circular linked lists is a singly linked list in which last node, next field points to first node in the sequence.
head | | +-----+--+ +-----+--+ +-----+--+ —> | 1 |o-----> | 2 |o-----> | 3 |o----| +-----+--+ +-----+--+ +-----+--+Timesharing problem solved by the operating system.
In a timesharing environment, the operating system must maintain a list of present users and must alternately allow each user to use a small portion of CPU time, one user at a time. The operating system will pick a user, let him/her use a small amount of CPU time and then move on to the next user.
For this application, there should be no NULL pointers unless there is absolutely no one requesting CPU time, i.e list is empty.
Linked List
- Linked List can be defined as collection of objects called nodes that are randomly stored in the memory.
- A node contains two fields i.e. data stored at that particular address and the pointer which contains the address of the next node in the memory.
- The last node of the list contains pointer to the null.
What is a singly linked list?
A singly linked list is a type of linked list that is unidirectional, that is, it can be traversed in only one direction from head to the last node (tail).
Each element in a linked list is called a node. A single node contains data and a pointer to the next node which helps in maintaining the structure of the list.
The first node is called the head; it points to the first node of the list and helps us access every other element in the list. The last node, also sometimes called the tail, points to NULL which helps us in determining when the list ends.
An example of a singly Linked List