Doubly linked list
Doubly linked list is a complex type of linked list in which a node contains a pointer to the previous as well as the next node in the sequence. Therefore, in a doubly linked list, a node consists of three parts: node data, pointer to the next node in sequence (next pointer) , pointer to the previous node (previous pointer). A sample node in a doubly linked list is shown in the figure.
A doubly linked list containing three nodes having numbers from 1 to 3 in their data part, is shown in the following image.
In C, structure of a node in doubly linked list can be given as :
The prev part of the first node and the next part of the last node will always contain null indicating end in each direction.
In a singly linked list, we could traverse only in one direction, because each node contains address of the next node and it doesn't have any record of its previous nodes. However, doubly linked list overcome this limitation of singly linked list. Due to the fact that, each node of the list contains the address of its previous node, we can find all the details about the previous node as well by using the previous address stored inside the previous part of each node.
Doubly Linked List
In this tutorial, you will learn about the doubly linke list and its implementation in Python, Java, C, and C++.
A doubly linked list is a type of linked list in which each node consists of 3 components:
- *prev - address of the previous node
- data - data item
- *next - address of next node
Note: Before you proceed further, make sure to learn about pointers and structs.
Doubly Linked List | Set 1 (Introduction and Insertion)
We strongly recommend to refer following post as a prerequisite of this post.
Linked List Introduction
Inserting a node in Singly Linked List
A Doubly Linked List (DLL) contains an extra pointer, typically called previous pointer, together with next pointer and data which are there in singly linked list.
Following is representation of a DLL node in C language.
C++
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/* Node of a doubly linked list */ class Node { public: int data; Node* next; // Pointer to next node in DLL Node* prev; // Pointer to previous node in DLL }; // This code is contributed by shivanisinghss2110 |
C
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/* Node of a doubly linked list */ struct Node { int data; struct Node* next; // Pointer to next node in DLL struct Node* prev; // Pointer to previous node in DLL }; |
Java
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// Class for Doubly Linked List public class DLL { Node head; // head of list /* Doubly Linked list Node*/ class Node { int data; Node prev; Node next; // Constructor to create a new node // next and prev is by default initialized as null Node(int d) { data = d; } } } |
Python3
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# Node of a doubly linked list class Node: def __init__(self, next=None, prev=None, data=None): self.next = next # reference to next node in DLL self.prev = prev # reference to previous node in DLL self.data = data |
C#
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// Class for Doubly Linked List public class DLL { Node head; // head of list /* Doubly Linked list Node*/ public class Node { public int data; public Node prev; public Node next; // Constructor to create a new node // next and prev is by default initialized as null Node(int d) { data = d; } } } // This code contributed by gauravrajput1 |
Javascript
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<script> // Class for Doubly Linked List var head; // head of list /* Doubly Linked list Node */ class Node { // Constructor to create a new node // next and prev is by default initialized as null constructor(val) { this.data = val; this.prev = null; this.next = null; } }
// This code contributed by gauravrajput1 </script> |
Following are advantages/disadvantages of doubly linked list over singly linked list.
Advantages over singly linked list
1) A DLL can be traversed in both forward and backward direction.
2) The delete operation in DLL is more efficient if pointer to the node to be deleted is given.
3) We can quickly insert a new node before a given node.
In singly linked list, to delete a node, pointer to the previous node is needed. To get this previous node, sometimes the list is traversed. In DLL, we can get the previous node using previous pointer.
Disadvantages over singly linked list
1) Every node of DLL Require extra space for an previous pointer. It is possible to implement DLL with single pointer though (See this and this).
2) All operations require an extra pointer previous to be maintained. For example, in insertion, we need to modify previous pointers together with next pointers. For example in following functions for insertions at different positions, we need 1 or 2 extra steps to set previous pointer.
Insertion
A node can be added in four ways
1) At the front of the DLL
2) After a given node.
3) At the end of the DLL
4) Before a given node.
Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.
1) Add a node at the front: (A 5 steps process)
The new node is always added before the head of the given Linked List. And newly added node becomes the new head of DLL. For example if the given Linked List is 10152025 and we add an item 5 at the front, then the Linked List becomes 510152025. Let us call the function that adds at the front of the list is push(). The push() must receive a pointer to the head pointer, because push must change the head pointer to point to the new node (See this)
Following are the 5 steps to add node at the front.
C++
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/* Given a reference (pointer to pointer) to the head of a list and an int, inserts a new node on the front of the list. */ void push(Node** head_ref, int new_data) { /* 1. allocate node */ Node* new_node = new Node(); /* 2. put in the data */ new_node->data = new_data; /* 3. Make next of new node as head and previous as NULL */ new_node->next = (*head_ref); new_node->prev = NULL; /* 4. change prev of head node to new node */ if ((*head_ref) != NULL) (*head_ref)->prev = new_node;
/* 5. move the head to point to the new node */ (*head_ref) = new_node; } // This code is contributed by shivanisinghss2110 |
C
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/* Given a reference (pointer to pointer) to the head of a list and an int, inserts a new node on the front of the list. */ void push(struct Node** head_ref, int new_data) { /* 1. allocate node */ struct Node* new_node = (struct Node*)malloc(sizeof(struct Node)); /* 2. put in the data */ new_node->data = new_data; /* 3. Make next of new node as head and previous as NULL */ new_node->next = (*head_ref); new_node->prev = NULL; /* 4. change prev of head node to new node */ if ((*head_ref) != NULL) (*head_ref)->prev = new_node; /* 5. move the head to point to the new node */ (*head_ref) = new_node; } |
Java
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// Adding a node at the front of the list public void push(int new_data) { /* 1. allocate node * 2. put in the data */ Node new_Node = new Node(new_data); /* 3. Make next of new node as head and previous as NULL */ new_Node.next = head; new_Node.prev = null; /* 4. change prev of head node to new node */ if (head != null) head.prev = new_Node; /* 5. move the head to point to the new node */ head = new_Node; } |
Python3
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# Adding a node at the front of the list def push(self, new_data): # 1 & 2: Allocate the Node & Put in the data new_node = Node(data = new_data) # 3. Make next of new node as head and previous as NULL new_node.next = self.head new_node.prev = None # 4. change prev of head node to new node if self.head is not None: self.head.prev = new_node # 5. move the head to point to the new node self.head = new_node # This code is contributed by jatinreaper |
C#
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// Adding a node at the front of the list public void push(int new_data) {
/* 1. allocate node * 2. put in the data */ Node new_Node = new Node(new_data); /* 3. Make next of new node as head and previous as NULL */ new_Node.next = head; new_Node.prev = null; /* 4. change prev of head node to new node */ if (head != null) head.prev = new_Node; /* 5. move the head to point to the new node */ head = new_Node; } // This code is contributed by aashish2995 |
Javascript
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// Adding a node at the front of the list function push(new_data) { /* 1. allocate node * 2. put in the data */ let new_Node = new Node(new_data); /* 3. Make next of new node as head and previous as NULL */ new_Node.next = head; new_Node.prev = null; /* 4. change prev of head node to new node */ if (head != null) head.prev = new_Node; /* 5. move the head to point to the new node */ head = new_Node; } // This code is contributed by saurabh_jaiswal. |
Four steps of the above five steps are same as the 4 steps used for inserting at the front in singly linked list. The only extra step is to change previous of head.
2) Add a node after a given node.: (A 7 steps process)
We are given pointer to a node as prev_node, and the new node is inserted after the given node.
C++
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/* Given a node as prev_node, insert a new node after the given node */ void insertAfter(Node* prev_node, int new_data) { /*1. check if the given prev_node is NULL */ if (prev_node == NULL) { cout<<"the given previous node cannot be NULL"; return; } /* 2. allocate new node */ Node* new_node = new Node(); /* 3. put in the data */ new_node->data = new_data; /* 4. Make next of new node as next of prev_node */ new_node->next = prev_node->next; /* 5. Make the next of prev_node as new_node */ prev_node->next = new_node; /* 6. Make prev_node as previous of new_node */ new_node->prev = prev_node; /* 7. Change previous of new_node's next node */ if (new_node->next != NULL) new_node->next->prev = new_node; } // This code is contributed by shivanisinghss2110. |
C
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/* Given a node as prev_node, insert a new node after the given node */ void insertAfter(struct Node* prev_node, int new_data) { /*1. check if the given prev_node is NULL */ if (prev_node == NULL) { printf("the given previous node cannot be NULL"); return; } /* 2. allocate new node */ struct Node* new_node = (struct Node*)malloc(sizeof(struct Node)); /* 3. put in the data */ new_node->data = new_data; /* 4. Make next of new node as next of prev_node */ new_node->next = prev_node->next; /* 5. Make the next of prev_node as new_node */ prev_node->next = new_node; /* 6. Make prev_node as previous of new_node */ new_node->prev = prev_node; /* 7. Change previous of new_node's next node */ if (new_node->next != NULL) new_node->next->prev = new_node; } |
Java
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/* Given a node as prev_node, insert a new node after the given node */ public void InsertAfter(Node prev_Node, int new_data) { /*1. check if the given prev_node is NULL */ if (prev_Node == null) { System.out.println("The given previous node cannot be NULL "); return; } /* 2. allocate node * 3. put in the data */ Node new_node = new Node(new_data); /* 4. Make next of new node as next of prev_node */ new_node.next = prev_Node.next; /* 5. Make the next of prev_node as new_node */ prev_Node.next = new_node; /* 6. Make prev_node as previous of new_node */ new_node.prev = prev_Node; /* 7. Change previous of new_node's next node */ if (new_node.next != null) new_node.next.prev = new_node; } |
Python3
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# Given a node as prev_node, insert # a new node after the given node def insertAfter(self, prev_node, new_data): # 1. check if the given prev_node is NULL if prev_node is None: print("This node doesn't exist in DLL") return #2. allocate node & 3. put in the data new_node = Node(data = new_data) # 4. Make next of new node as next of prev_node new_node.next = prev_node.next # 5. Make the next of prev_node as new_node prev_node.next = new_node # 6. Make prev_node as previous of new_node new_node.prev = prev_node # 7. Change previous of new_node's next node */ if new_node.next is not None: new_node.next.prev = new_node # This code is contributed by jatinreaper |
C#
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/* Given a node as prev_node, insert a new node after the given node */ public void InsertAfter(Node prev_Node, int new_data) { /*1. check if the given prev_node is NULL */ if (prev_Node == null) { Console.WriteLine("The given previous node cannot be NULL "); return; } /* 2. allocate node * 3. put in the data */ Node new_node = new Node(new_data); /* 4. Make next of new node as next of prev_node */ new_node.next = prev_Node.next; /* 5. Make the next of prev_node as new_node */ prev_Node.next = new_node; /* 6. Make prev_node as previous of new_node */ new_node.prev = prev_Node; /* 7. Change previous of new_node's next node */ if (new_node.next != null) new_node.next.prev = new_node; } // This code is contributed by aashish2995 |
Javascript
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<script> function InsertAfter(prev_Node,new_data) { /*1. check if the given prev_node is NULL */ if (prev_Node == null) { document.write("The given previous node cannot be NULL <br>"); return; } /* 2. allocate node * 3. put in the data */ let new_node = new Node(new_data); /* 4. Make next of new node as next of prev_node */ new_node.next = prev_Node.next; /* 5. Make the next of prev_node as new_node */ prev_Node.next = new_node; /* 6. Make prev_node as previous of new_node */ new_node.prev = prev_Node; /* 7. Change previous of new_node's next node */ if (new_node.next != null) new_node.next.prev = new_node; } // This code is contributed by unknown2108 </script> |
Five of the above steps step process are same as the 5 steps used for inserting after a given node in singly linked list. The two extra steps are needed to change previous pointer of new node and previous pointer of new node’s next node.
3) Add a node at the end: (7 steps process)
The new node is always added after the last node of the given Linked List. For example if the given DLL is 510152025 and we add an item 30 at the end, then the DLL becomes 51015202530.
Since a Linked List is typically represented by the head of it, we have to traverse the list till end and then change the next of last node to new node.
Following are the 7 steps to add node at the end.
C++
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/* Given a reference (pointer to pointer) to the head of a DLL and an int, appends a new node at the end */ void append(Node** head_ref, int new_data) { /* 1. allocate node */ Node* new_node = new Node(); Node* last = *head_ref; /* used in step 5*/ /* 2. put in the data */ new_node->data = new_data; /* 3. This new node is going to be the last node, so make next of it as NULL*/ new_node->next = NULL; /* 4. If the Linked List is empty, then make the new node as head */ if (*head_ref == NULL) { new_node->prev = NULL; *head_ref = new_node; return; } /* 5. Else traverse till the last node */ while (last->next != NULL) last = last->next; /* 6. Change the next of last node */ last->next = new_node; /* 7. Make last node as previous of new node */ new_node->prev = last; return; } // This code is contributed by shivanisinghss2110 |
C
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/* Given a reference (pointer to pointer) to the head of a DLL and an int, appends a new node at the end */ void append(struct Node** head_ref, int new_data) { /* 1. allocate node */ struct Node* new_node = (struct Node*)malloc(sizeof(struct Node)); struct Node* last = *head_ref; /* used in step 5*/ /* 2. put in the data */ new_node->data = new_data; /* 3. This new node is going to be the last node, so make next of it as NULL*/ new_node->next = NULL; /* 4. If the Linked List is empty, then make the new node as head */ if (*head_ref == NULL) { new_node->prev = NULL; *head_ref = new_node; return; } /* 5. Else traverse till the last node */ while (last->next != NULL) last = last->next; /* 6. Change the next of last node */ last->next = new_node; /* 7. Make last node as previous of new node */ new_node->prev = last; return; } |
Java
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// Add a node at the end of the list void append(int new_data) { /* 1. allocate node * 2. put in the data */ Node new_node = new Node(new_data); Node last = head; /* used in step 5*/ /* 3. This new node is going to be the last node, so * make next of it as NULL*/ new_node.next = null; /* 4. If the Linked List is empty, then make the new * node as head */ if (head == null) { new_node.prev = null; head = new_node; return; } /* 5. Else traverse till the last node */ while (last.next != null) last = last.next; /* 6. Change the next of last node */ last.next = new_node; /* 7. Make last node as previous of new node */ new_node.prev = last; } |
Python3
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# Add a node at the end of the DLL def append(self, new_data): # 1. allocate node 2. put in the data new_node = Node(data = new_data) last = self.head # 3. This new node is going to be the # last node, so make next of it as NULL new_node.next = None # 4. If the Linked List is empty, then # make the new node as head if self.head is None: new_node.prev = None self.head = new_node return # 5. Else traverse till the last node while (last.next is not None): last = last.next # 6. Change the next of last node last.next = new_node # 7. Make last node as previous of new node */ new_node.prev = last # This code is contributed by jatinreaper |
C#
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// Add a node at the end of the list void append(int new_data) { /* 1. allocate node * 2. put in the data */ Node new_node = new Node(new_data); Node last = head; /* used in step 5*/ /* 3. This new node is going to be the last node, so * make next of it as NULL*/ new_node.next = null;
/* 4. If the Linked List is empty, then make the new * node as head */ if (head == null) { new_node.prev = null; head = new_node; return; } /* 5. Else traverse till the last node */ while (last.next != null) last = last.next; /* 6. Change the next of last node */ last.next = new_node; /* 7. Make last node as previous of new node */ new_node.prev = last; } // This code is contributed by shivanisinghss2110 |
Javascript
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<script> // Add a node at the end of the list function append(new_data) { /* 1. allocate node * 2. put in the data */ var new_node = new Node(new_data); var last = head; /* used in step 5*/ /* 3. This new node is going to be the last node, so * make next of it as NULL*/ new_node.next = null; /* 4. If the Linked List is empty, then make the new * node as head */ if (head == null) { new_node.prev = null; head = new_node; return; } /* 5. Else traverse till the last node */ while (last.next != null) last = last.next; /* 6. Change the next of last node */ last.next = new_node; /* 7. Make last node as previous of new node */ new_node.prev = last; } // This code is contributed by Rajput-Ji </script> |
Six of the above 7 steps are same as the 6 steps used for inserting after a given node in singly linked list. The one extra step is needed to change previous pointer of new node.
4) Add a node before a given node:
Steps
Let the pointer to this given node be next_node and the data of the new node to be added as new_data.
- Check if the next_node is NULL or not. If it’s NULL, return from the function because any new node can not be added before a NULL
- Allocate memory for the new node, let it be called new_node
- Set new_node->data = new_data
- Set the previous pointer of this new_node as the previous node of the next_node, new_node->prev = next_node->prev
- Set the previous pointer of the next_node as the new_node, next_node->prev = new_node
- Set the next pointer of this new_node as the next_node, new_node->next = next_node;
- If the previous node of the new_node is not NULL, then set the next pointer of this previous node as new_node, new_node->prev->next = new_node
- Else, if the prev of new_node is NULL, it will be the new head node. So, make (*head_ref) = new_node.
Below is the implementation of the above approach:
Code block
Output:
Created DLL is:
Traversal in forward Direction
9 1 5 7 6
Traversal in reverse direction
6 7 5 1 9
A complete working program to test above functions.
Following is complete program to test above functions.
C++
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// A complete working C++ program to // demonstrate all insertion methods #include <bits/stdc++.h> using namespace std; // A linked list node class Node { public: int data; Node* next; Node* prev; }; /* Given a reference (pointer to pointer) to the head of a list and an int, inserts a new node on the front of the list. */ void push(Node** head_ref, int new_data) { /* 1. allocate node */ Node* new_node = new Node(); /* 2. put in the data */ new_node->data = new_data; /* 3. Make next of new node as head and previous as NULL */ new_node->next = (*head_ref); new_node->prev = NULL; /* 4. change prev of head node to new node */ if ((*head_ref) != NULL) (*head_ref)->prev = new_node; /* 5. move the head to point to the new node */ (*head_ref) = new_node; } /* Given a node as prev_node, insert a new node after the given node */ void insertAfter(Node* prev_node, int new_data) { /*1. check if the given prev_node is NULL */ if (prev_node == NULL) { cout<<"the given previous node cannot be NULL"; return; } /* 2. allocate new node */ Node* new_node = new Node(); /* 3. put in the data */ new_node->data = new_data; /* 4. Make next of new node as next of prev_node */ new_node->next = prev_node->next; /* 5. Make the next of prev_node as new_node */ prev_node->next = new_node; /* 6. Make prev_node as previous of new_node */ new_node->prev = prev_node; /* 7. Change previous of new_node's next node */ if (new_node->next != NULL) new_node->next->prev = new_node; } /* Given a reference (pointer to pointer) to the head of a DLL and an int, appends a new node at the end */ void append(Node** head_ref, int new_data) { /* 1. allocate node */ Node* new_node = new Node(); Node* last = *head_ref; /* used in step 5*/ /* 2. put in the data */ new_node->data = new_data; /* 3. This new node is going to be the last node, so make next of it as NULL*/ new_node->next = NULL; /* 4. If the Linked List is empty, then make the new node as head */ if (*head_ref == NULL) { new_node->prev = NULL; *head_ref = new_node; return; } /* 5. Else traverse till the last node */ while (last->next != NULL) last = last->next; /* 6. Change the next of last node */ last->next = new_node; /* 7. Make last node as previous of new node */ new_node->prev = last; return; } // This function prints contents of // linked list starting from the given node void printList(Node* node) { Node* last; cout<<"\nTraversal in forward direction \n"; while (node != NULL) { cout<<" "<<node->data<<" "; last = node; node = node->next; } cout<<"\nTraversal in reverse direction \n"; while (last != NULL) { cout<<" "<<last->data<<" "; last = last->prev; } } /* Driver program to test above functions*/ int main() { /* Start with the empty list */ Node* head = NULL; // Insert 6. So linked list becomes 6->NULL append(&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); // Insert 4 at the end. So linked // list becomes 1->7->6->4->NULL append(&head, 4); // Insert 8, after 7. So linked // list becomes 1->7->8->6->4->NULL insertAfter(head->next, 8); cout << "Created DLL is: "; printList(head); return 0; } // This is code is contributed by rathbhupendra |
C
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// A complete working C program to // demonstrate all insertion // methods #include <stdio.h> #include <stdlib.h> // A linked list node struct Node { int data; struct Node* next; struct Node* prev; }; /* Given a reference (pointer to pointer) to the head of a list and an int, inserts a new node on the front of the list. */ void push(struct Node** head_ref, int new_data) { /* 1. allocate node */ struct Node* new_node = (struct Node*)malloc(sizeof(struct Node)); /* 2. put in the data */ new_node->data = new_data; /* 3. Make next of new node as head and previous as NULL */ new_node->next = (*head_ref); new_node->prev = NULL; /* 4. change prev of head node to new node */ if ((*head_ref) != NULL) (*head_ref)->prev = new_node; /* 5. move the head to point to the new node */ (*head_ref) = new_node; } /* Given a node as prev_node, insert a new node after the * given node */ void insertAfter(struct Node* prev_node, int new_data) { /*1. check if the given prev_node is NULL */ if (prev_node == NULL) { printf("the given previous node cannot be NULL"); return; } /* 2. allocate new node */ struct Node* new_node = (struct Node*)malloc(sizeof(struct Node)); /* 3. put in the data */ new_node->data = new_data; /* 4. Make next of new node as next of prev_node */ new_node->next = prev_node->next; /* 5. Make the next of prev_node as new_node */ prev_node->next = new_node; /* 6. Make prev_node as previous of new_node */ new_node->prev = prev_node; /* 7. Change previous of new_node's next node */ if (new_node->next != NULL) new_node->next->prev = new_node; } /* Given a reference (pointer to pointer) to the head of a DLL and an int, appends a new node at the end */ void append(struct Node** head_ref, int new_data) { /* 1. allocate node */ struct Node* new_node = (struct Node*)malloc(sizeof(struct Node)); struct Node* last = *head_ref; /* used in step 5*/ /* 2. put in the data */ new_node->data = new_data; /* 3. This new node is going to be the last node, so make next of it as NULL*/ new_node->next = NULL; /* 4. If the Linked List is empty, then make the new node as head */ if (*head_ref == NULL) { new_node->prev = NULL; *head_ref = new_node; return; } /* 5. Else traverse till the last node */ while (last->next != NULL) last = last->next; /* 6. Change the next of last node */ last->next = new_node; /* 7. Make last node as previous of new node */ new_node->prev = last; return; } // This function prints contents of linked list starting // from the given node void printList(struct Node* node) { struct Node* last; printf("\nTraversal in forward direction \n"); while (node != NULL) { printf(" %d ", node->data); last = node; node = node->next; } printf("\nTraversal in reverse direction \n"); while (last != NULL) { printf(" %d ", last->data); last = last->prev; } } /* Driver program to test above functions*/ int main() { /* Start with the empty list */ struct Node* head = NULL; // Insert 6. So linked list becomes 6->NULL append(&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); // Insert 4 at the end. So linked list becomes // 1->7->6->4->NULL append(&head, 4); // Insert 8, after 7. So linked list becomes // 1->7->8->6->4->NULL insertAfter(head->next, 8); printf("Created DLL is: "); printList(head); getchar(); return 0; } |
Java
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// A complete working Java program to demonstrate all // Class for Doubly Linked List public class DLL { Node head; // head of list /* Doubly Linked list Node*/ class Node { int data; Node prev; Node next; // Constructor to create a new node // next and prev is by default initialized as null Node(int d) { data = d; } } // Adding a node at the front of the list public void push(int new_data) { /* 1. allocate node * 2. put in the data */ Node new_Node = new Node(new_data); /* 3. Make next of new node as head and previous as NULL */ new_Node.next = head; new_Node.prev = null; /* 4. change prev of head node to new node */ if (head != null) head.prev = new_Node; /* 5. move the head to point to the new node */ head = new_Node; }
// Add a node before the given node public void InsertBefore(Node next_node, int new_data) { /*Check if the given nx_node is NULL*/ if(next_node == null) { System.out.println("The given next node can not be NULL"); return; }
//Allocate node, put in the data Node new_node = new Node(new_data);
//Making prev of new node as prev of next node new_node.prev = next_node.prev;
//Making prev of next node as new node next_node.prev = new_node;
//Making next of new node as next node new_node.next = next_node;
//Check if new node is added as head if(new_node.prev != null) new_node.prev.next = new_node; else head = new_node; } /* Given a node as prev_node, insert a new node after the given node */ public void InsertAfter(Node prev_Node, int new_data) { /*1. check if the given prev_node is NULL */ if (prev_Node == null) { System.out.println("The given previous node cannot be NULL "); return; } /* 2. allocate node * 3. put in the data */ Node new_node = new Node(new_data); /* 4. Make next of new node as next of prev_node */ new_node.next = prev_Node.next; /* 5. Make the next of prev_node as new_node */ prev_Node.next = new_node; /* 6. Make prev_node as previous of new_node */ new_node.prev = prev_Node; /* 7. Change previous of new_node's next node */ if (new_node.next != null) new_node.next.prev = new_node; } // Add a node at the end of the list void append(int new_data) { /* 1. allocate node * 2. put in the data */ Node new_node = new Node(new_data); Node last = head; /* used in step 5*/ /* 3. This new node is going to be the last node, so * make next of it as NULL*/ new_node.next = null; /* 4. If the Linked List is empty, then make the new * node as head */ if (head == null) { new_node.prev = null; head = new_node; return; } /* 5. Else traverse till the last node */ while (last.next != null) last = last.next; /* 6. Change the next of last node */ last.next = new_node; /* 7. Make last node as previous of new node */ new_node.prev = last; } // This function prints contents of // linked list starting from the given node public void printlist(Node node) { Node last = null; System.out.println("Traversal in forward Direction"); while (node != null) { System.out.print(node.data + " "); last = node; node = node.next; } System.out.println(); System.out.println("Traversal in reverse direction"); while (last != null) { System.out.print(last.data + " "); last = last.prev; } } /* Driver program to test above functions*/ public static void main(String[] args) { /* Start with the empty list */ DLL dll = new DLL(); // Insert 6. So linked list becomes 6->NULL dll.append(6); // Insert 7 at the beginning. So // linked list becomes 7->6->NULL dll.push(7); // Insert 1 at the beginning. So // linked list becomes 1->7->6->NULL dll.push(1); // Insert 4 at the end. So linked // list becomes 1->7->6->4->NULL dll.append(4); // Insert 8, after 7. So linked // list becomes 1->7->8->6->4->NULL dll.InsertAfter(dll.head.next, 8);
// Insert 5, before 8.So linked // list becomes 1->7->5->8->6->4 dll.InsertBefore(dll.head.next.next, 5); System.out.println("Created DLL is: "); dll.printlist(dll.head); } } // This code is contributed by Sumit Ghosh |
Python3
|
# A complete working Python # program to demonstrate all # insertion methods # A linked list node class Node: # Constructor to create a new node def __init__(self, data): self.data = data self.next = None self.prev = None # Class to create a Doubly Linked List class DoublyLinkedList: # Constructor for empty Doubly Linked List def __init__(self): self.head = None # Given a reference to the head of a list and an # integer, inserts a new node on the front of list def push(self, new_data): # 1. Allocates node # 2. Put the data in it new_node = Node(new_data) # 3. Make next of new node as head and # previous as None (already None) new_node.next = self.head # 4. change prev of head node to new_node if self.head is not None: self.head.prev = new_node # 5. move the head to point to the new node self.head = new_node # Given a node as prev_node, insert a new node after # the given node def insertAfter(self, prev_node, new_data): # 1. Check if the given prev_node is None if prev_node is None: print("the given previous node cannot be NULL") return # 2. allocate new node # 3. put in the data new_node = Node(new_data) # 4. Make net of new node as next of prev node new_node.next = prev_node.next # 5. Make prev_node as previous of new_node prev_node.next = new_node # 6. Make prev_node ass previous of new_node new_node.prev = prev_node # 7. Change previous of new_nodes's next node if new_node.next: new_node.next.prev = new_node # Given a reference to the head of DLL and integer, # appends a new node at the end def append(self, new_data): # 1. Allocates node # 2. Put in the data new_node = Node(new_data) # 3. This new node is going to be the last node, # so make next of it as None # (It already is initialized as None) # 4. If the Linked List is empty, then make the # new node as head if self.head is None: self.head = new_node return # 5. Else traverse till the last node last = self.head while last.next: last = last.next # 6. Change the next of last node last.next = new_node # 7. Make last node as previous of new node new_node.prev = last return # This function prints contents of linked list # starting from the given node def printList(self, node): print("\nTraversal in forward direction") while node: print(" {}".format(node.data)) last = node node = node.next print("\nTraversal in reverse direction") while last: print(" {}".format(last.data)) last = last.prev # Driver program to test above functions # Start with empty list llist = DoublyLinkedList() # Insert 6. So the list becomes 6->None llist.append(6) # Insert 7 at the beginning. # So linked list becomes 7->6->None llist.push(7) # Insert 1 at the beginning. # So linked list becomes 1->7->6->None llist.push(1) # Insert 4 at the end. # So linked list becomes 1->7->6->4->None llist.append(4) # Insert 8, after 7. # So linked list becomes 1->7->8->6->4->None llist.insertAfter(llist.head.next, 8) print ("Created DLL is: ") llist.printList(llist.head) # This code is contributed by Nikhil Kumar Singh(nickzuck_007) |
C#
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// A complete working C# program to demonstrate all using System; // Class for Doubly Linked List public class DLL { Node head; // head of list /* Doubly Linked list Node*/ public class Node { public int data; public Node prev; public Node next; // Constructor to create a new node // next and prev is by default initialized as null public Node(int d) { data = d; } } // Adding a node at the front of the list public void push(int new_data) { /* 1. allocate node * 2. put in the data */ Node new_Node = new Node(new_data); /* 3. Make next of new node as head and previous as NULL */ new_Node.next = head; new_Node.prev = null; /* 4. change prev of head node to new node */ if (head != null) head.prev = new_Node; /* 5. move the head to point to the new node */ head = new_Node; } /* Given a node as prev_node, insert a new node after the given node */ public void InsertAfter(Node prev_Node, int new_data) { /*1. check if the given prev_node is NULL */ if (prev_Node == null) { Console.WriteLine("The given previous node cannot be NULL "); return; } /* 2. allocate node * 3. put in the data */ Node new_node = new Node(new_data); /* 4. Make next of new node as next of prev_node */ new_node.next = prev_Node.next; /* 5. Make the next of prev_node as new_node */ prev_Node.next = new_node; /* 6. Make prev_node as previous of new_node */ new_node.prev = prev_Node; /* 7. Change previous of new_node's next node */ if (new_node.next != null) new_node.next.prev = new_node; } // Add a node at the end of the list void append(int new_data) { /* 1. allocate node * 2. put in the data */ Node new_node = new Node(new_data); Node last = head; /* used in step 5*/ /* 3. This new node is going to be the last node, so * make next of it as NULL*/ new_node.next = null; /* 4. If the Linked List is empty, then make the new * node as head */ if (head == null) { new_node.prev = null; head = new_node; return; } /* 5. Else traverse till the last node */ while (last.next != null) last = last.next; /* 6. Change the next of last node */ last.next = new_node; /* 7. Make last node as previous of new node */ new_node.prev = last; } // This function prints contents of // linked list starting from the given node public void printlist(Node node) { Node last = null; Console.WriteLine("Traversal in forward Direction"); while (node != null) { Console.Write(node.data + " "); last = node; node = node.next; } Console.WriteLine(); Console.WriteLine("Traversal in reverse direction"); while (last != null) { Console.Write(last.data + " "); last = last.prev; } } /* Driver code*/ public static void Main(String[] args) { /* Start with the empty list */ DLL dll = new DLL(); // Insert 6. So linked list becomes 6->NULL dll.append(6); // Insert 7 at the beginning. // So linked list becomes 7->6->NULL dll.push(7); // Insert 1 at the beginning. // So linked list becomes 1->7->6->NULL dll.push(1); // Insert 4 at the end. So linked list // becomes 1->7->6->4->NULL dll.append(4); // Insert 8, after 7. So linked list // becomes 1->7->8->6->4->NULL dll.InsertAfter(dll.head.next, 8); Console.WriteLine("Created DLL is: "); dll.printlist(dll.head); } } // This code is contributed by 29AjayKumar |
Javascript
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<script> // A complete working javascript program to demonstrate all // Class for Doubly Linked List var head; // head of list /* Doubly Linked list Node */ class Node { // Constructor to create a new node // next and prev is by default initialized as null constructor(d) { this.data = d; this.next = null; this.prev = null; } } // Adding a node at the front of the list function push(new_data) { /* * 1. allocate node 2. put in the data */ var new_Node = new Node(new_data); /* 3. Make next of new node as head and previous as NULL */ new_Node.next = head; new_Node.prev = null; /* 4. change prev of head node to new node */ if (head != null) head.prev = new_Node; /* 5. move the head to point to the new node */ head = new_Node; } // Add a node before the given node function InsertBefore(next_node , new_data) { /* Check if the given nx_node is NULL */ if (next_node == null) { document.write("The given next node can not be NULL"); return; } // Allocate node, put in the data var new_node = new Node(new_data); // Making prev of new node as prev of next node new_node.prev = next_node.prev; // Making prev of next node as new node next_node.prev = new_node; // Making next of new node as next node new_node.next = next_node; // Check if new node is added as head if (new_node.prev != null) new_node.prev.next = new_node; else head = new_node; } /* * Given a node as prev_node, insert a new node after the given node */ function InsertAfter(prev_Node , new_data) { /* 1. check if the given prev_node is NULL */ if (prev_Node == null) { document.write("The given previous node cannot be NULL "); return; } /* * 2. allocate node 3. put in the data */ var new_node = new Node(new_data); /* 4. Make next of new node as next of prev_node */ new_node.next = prev_Node.next; /* 5. Make the next of prev_node as new_node */ prev_Node.next = new_node; /* 6. Make prev_node as previous of new_node */ new_node.prev = prev_Node; /* 7. Change previous of new_node's next node */ if (new_node.next != null) new_node.next.prev = new_node; } // Add a node at the end of the list function append(new_data) { /* * 1. allocate node 2. put in the data */ var new_node = new Node(new_data); var last = head; /* used in step 5 */ /* * 3. This new node is going to be the last node, so make next of it as NULL */ new_node.next = null; /* * 4. If the Linked List is empty, then make the new node as head */ if (head == null) { new_node.prev = null; head = new_node; return; } /* 5. Else traverse till the last node */ while (last.next != null) last = last.next; /* 6. Change the next of last node */ last.next = new_node; /* 7. Make last node as previous of new node */ new_node.prev = last; } // This function prints contents of // linked list starting from the given node function printlist(node) { var last = null; document.write("<br/>Traversal in forward Direction<br/>"); while (node != null) { document.write(node.data + " "); last = node; node = node.next; } document.write(); document.write("<br/>Traversal in reverse direction<br/>"); while (last != null) { document.write(last.data + " "); last = last.prev; } } /* Driver program to test above functions */
/* Start with the empty list */
// Insert 6. So linked list becomes 6->NULL append(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); // Insert 4 at the end. So linked // list becomes 1->7->6->4->NULL append(4); // Insert 8, after 7. So linked // list becomes 1->7->8->6->4->NULL InsertAfter(head.next, 8); // Insert 5, before 8.So linked // list becomes 1->7->5->8->6->4 InsertBefore(head.next.next, 5); document.write("Created DLL is:<br/> "); printlist(head); // This code is contributed by Rajput-Ji </script> |
Output:
Created DLL is: Traversal in forward Direction 1 7 5 8 6 4 Traversal in reverse direction 4 6 8 5 7 1Also see: Delete a node in double Link List
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Menu driven program for all operations on doubly linked list in C
A Linked List is a linear data structure that consists of two parts: one is the data part and the other is the address part. A Doubly Linked List in contains three parts: one is the data part and the other two are the address of the next and previous node in the list. In this article, all the common operations of a doubly linked list is discussed in one menu-driven program.
Operations to be performed:
- traverse(): To see the contents of the linked list, it is necessary to traverse the given doubly linked list. The given traverse() function traverses and prints the content of the doubly linked list.
- insertAtFront(): This function simply inserts an element at the front/beginning of the doubly linked list.
- insertAtEnd(): This function inserts an element at the end of the doubly linked list.
- insertAtPosition(): This function inserts an element at a specified position in the doubly linked list.
- deleteFirst(): This function simply deletes an element from the front/beginning of the doubly linked list.
- deleteEnd(): This function simply deletes an element from the end of the doubly linked list.
- deletePosition(): This function deletes an element from a specified position in the doubly linked list.
Below is the implementation of the above operations:
C
|
// C program for the all operations in // the Doubly Linked List #include <stdio.h> #include <stdlib.h> // Linked List Node struct node { int info; struct node *prev, *next; }; struct node* start = NULL; // Function to traverse the linked list void traverse() { // List is empty if (start == NULL) { printf("\nList is empty\n"); return; } // Else print the Data struct node* temp; temp = start; while (temp != NULL) { printf("Data = %d\n", temp->info); temp = temp->next; } } // Function to insert at the front // of the linked list void insertAtFront() { int data; struct node* temp; temp = (struct node*)malloc(sizeof(struct node)); printf("\nEnter number to be inserted: "); scanf("%d", &data); temp->info = data; temp->prev = NULL; // Pointer of temp will be // assigned to start temp->next = start; start = temp; } // Function to insert at the end of // the linked list void insertAtEnd() { int data; struct node *temp, *trav; temp = (struct node*)malloc(sizeof(struct node)); temp->prev = NULL; temp->next = NULL; printf("\nEnter number to be inserted: "); scanf("%d", &data); temp->info = data; temp->next = NULL; trav = start; // If start is NULL if (start == NULL) { start = temp; } // Changes Links else { while (trav->next != NULL) trav = trav->next; temp->prev = trav; trav->next = temp; } } // Function to insert at any specified // position in the linked list void insertAtPosition() { int data, pos, i = 1; struct node *temp, *newnode; newnode = malloc(sizeof(struct node)); newnode->next = NULL; newnode->prev = NULL; // Enter the position and data printf("\nEnter position : "); scanf("%d", &pos);
// If start==NULL, if (start == NULL) { start = newnode; newnode->prev = NULL; newnode->next = NULL; } // If position==1, else if (pos == 1) { // this is author method its correct but we can simply call insertAtfront() function for this special case /* newnode->next = start; newnode->next->prev = newnode; newnode->prev = NULL; start = newnode; */ // now this is improved by Jay Ghughriwala on geeksforgeeks insertAtFront(); } // Change links else { printf("\nEnter number to be inserted: "); scanf("%d", &data); newnode->info = data; temp = start; while (i < pos - 1) { temp = temp->next; i++; } newnode->next = temp->next; newnode->prev = temp; temp->next = newnode; temp->next->prev = newnode; } } // Function to delete from the front // of the linked list void deleteFirst() { struct node* temp; if (start == NULL) printf("\nList is empty\n"); else { temp = start; start = start->next; if (start != NULL) start->prev = NULL; free(temp); } } // Function to delete from the end // of the linked list void deleteEnd() { struct node* temp; if (start == NULL) printf("\nList is empty\n"); temp = start; while (temp->next != NULL) temp = temp->next; if (start->next == NULL) start = NULL; else { temp->prev->next = NULL; free(temp); } } // Function to delete from any specified // position from the linked list void deletePosition() { int pos, i = 1; struct node *temp, *position; temp = start; // If DLL is empty if (start == NULL) printf("\nList is empty\n"); // Otherwise else { // Position to be deleted printf("\nEnter position : "); scanf("%d", &pos); // If the position is the first node if (pos == 1) { deleteFirst(); // im,proved by Jay Ghughriwala on GeeksforGeeks if (start != NULL) { start->prev = NULL; } free(position); return; } // Traverse till position while (i < pos - 1) { temp = temp->next; i++; } // Change Links position = temp->next; if (position->next != NULL) position->next->prev = temp; temp->next = position->next; // Free memory free(position); } } // Driver Code int main() { int choice; while (1) { printf("\n\t1 To see list\n"); printf("\t2 For insertion at" " starting\n"); printf("\t3 For insertion at" " end\n"); printf("\t4 For insertion at " "any position\n"); printf("\t5 For deletion of " "first element\n"); printf("\t6 For deletion of " "last element\n"); printf("\t7 For deletion of " "element at any position\n"); printf("\t8 To exit\n"); printf("\nEnter Choice :\n"); scanf("%d", &choice); switch (choice) { case 1: traverse(); break; case 2: insertAtFront(); break; case 3: insertAtEnd(); break; case 4: insertAtPosition(); break; case 5: deleteFirst(); break; case 6: deleteEnd(); break; case 7: deletePosition(); break; case 8: exit(1); break; default: printf("Incorrect Choice. Try Again \n"); continue; } } return 0; } |
Output:
Menu:
Insertion at the starting:
Insertion at the end:
Insertion at specific position:
Print the Linked List:
Delete the first and last element with choice 5 and 6:
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Doubly Linked List Program in C
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Doubly Linked List is a variation of Linked list in which navigation is possible in both ways, either forward and backward easily as compared to Single Linked List.