Doubly Linked List implementation in C

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               Doubly linked list is a type of linked list. It can traverse in both directions. The operations of doubly linked list are given below.

  • ·       Creation of node.
  • ·       Insert the data at the beginning.
  • ·       Insert the data at the end.
  • ·       Delete the data at the beginning.
  • ·       Delete the data at the end.
  • ·       Delete a data based on the value.
  • ·       Traverse data in the forward direction.
  • ·       Traverse data in the backward direction.

C Code:

#include <stdio.h>

#include <stdlib.h>

// Define the structure for a doubly linked list node

struct Node {

    int data;

    struct Node* l_prev;

    struct Node* l_next;

};

// Creation of a new node

struct Node* createNode(int value) {

    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));

    newNode->data = value;

    newNode->l_prev = NULL;

    newNode->l_next = NULL;

    return newNode;

}

// traverse in forward

void traverse_Forward(struct Node* head) {

    struct Node* temp = head;

    printf("Forward->: ");

    while (temp != NULL) {

        printf("%d <-> ", temp->data);

        temp = temp->l_next;

    }

    printf("NULL\n");

}

// traverse in backward

void traverse_Backward(struct Node* tail) {

    struct Node* temp = tail;

    printf("Backward <---: ");

    while (temp != NULL) {

        printf("%d <-> ", temp->data);

        temp = temp->l_prev;

    }

    printf("NULL\n");

}

// Insert the data in the beginning

struct Node* insertAt_Beginning(struct Node* head, int value) {

    struct Node* newNode = createNode(value);

    if (head != NULL) {

        newNode->l_next = head;

        head->l_prev = newNode;

    }

    return newNode; // new head

}

// Insert the data at the end

struct Node* insertAt_End(struct Node* head, int value) {

    struct Node* newNode = createNode(value);

    if (head == NULL) return newNode;

     struct Node* temp = head;

    while (temp->l_next != NULL) {

        temp = temp->l_next;

    }

    temp->l_next = newNode;

    newNode->l_prev = temp;

    return head;

}

// Delete the data from beginning

struct Node* delete_FromBeginning(struct Node* head) {

    if (head == NULL) return NULL;

    struct Node* temp = head;

    head = head->l_next;

    if (head != NULL) head->l_prev = NULL;

    free(temp);

    return head;

}

// Delete the data from end

struct Node* delete_FromEnd(struct Node* head) {

    if (head == NULL) return NULL;

    struct Node* temp = head;

    while (temp->l_next != NULL) {

        temp = temp->l_next;

    }

    if (temp->l_prev != NULL) {

        temp->l_prev->l_next = NULL;

    } else {

        head = NULL; // list had only one node

    }

    free(temp);

    return head;

}

// Delete a node by using the value

struct Node* delete_ByValue(struct Node* head, int value) {

    struct Node* temp = head;

    while (temp != NULL && temp->data != value) {

        temp = temp->l_next;

    }

    if (temp == NULL) return head; // value not found

    if (temp->l_prev != NULL) temp->l_prev->l_next = temp->l_next;

    else head = temp->l_next; // deleting head

    if (temp->l_next != NULL) temp->l_next->l_prev = temp->l_prev;

    free(temp);

    return head;

}

int main() {

    struct Node* head = NULL;

    // Insert nodes

    head = insertAt_End(head, 100);

    head = insertAt_End(head, 120);

    head = insertAt_End(head, 31);

    head = insertAt_End(head, 43);

    head = insertAt_End(head, 90);

    traverse_Forward(head);

    // Insert the data at beginning

    head = insertAt_Beginning(head, 5);

    traverse_Forward(head);

    // Delete the data from beginning

    head = delete_FromBeginning(head);

    traverse_Forward(head);

    // Delete the data from end

    head = delete_FromEnd(head);

    traverse_Forward(head);

    // Delete the node by value

    head = delete_ByValue(head, 20);

    traverse_Forward(head);

    return 0;

}

Output:

Forward->: 100 <-> 120 <-> 31 <-> 43 <-> 90 <-> NULL

Forward->: 5 <-> 100 <-> 120 <-> 31 <-> 43 <-> 90 <-> NULL

Forward->: 100 <-> 120 <-> 31 <-> 43 <-> 90 <-> NULL

Forward->: 100 <-> 120 <-> 31 <-> 43 <-> NULL

Forward->: 100 <-> 120 <-> 31 <-> 43 <-> NULL

This is the way of implementing Doubly Linked list in C. Hope, you understood it. Keep Coding!!!

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