C Program For Deleting A Node In A Linked List

Last Updated : 17 Aug, 2023

We have discussed Linked List Introduction and Linked List Insertion in previous posts on a singly linked list.
Let us formulate the problem statement to understand the deletion process. Given a 'key', delete the first occurrence of this key in the linked list.

Iterative Method:
To delete a node from the linked list, we need to do the following steps.
1) Find the previous node of the node to be deleted.
2) Change the next of the previous node.
3) Free memory for the node to be deleted.

linkedlist_deletion

Since every node of the linked list is dynamically allocated using malloc() in C, we need to call free() for freeing memory allocated for the node to be deleted.

// A complete working C program
// to demonstrate deletion in
// singly linked list
#include <stdio.h>
#include <stdlib.h>

// A linked list node
struct Node {
    int data;
    struct Node* next;
};

/* 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)
{
    struct Node* new_node
        = (struct Node*)malloc(sizeof(struct Node));
    new_node->data = new_data;
    new_node->next = (*head_ref);
    (*head_ref) = new_node;
}

/* Given a reference (pointer to pointer) to the head of a
   list and a key, deletes the first occurrence of key in
   linked list */
void deleteNode(struct Node** head_ref, int key)
{
    // Store head node
    struct Node *temp = *head_ref, *prev;

    // If head node itself holds the key to be deleted
    if (temp != NULL && temp->data == key) {
        *head_ref = temp->next; // Changed head
        free(temp); // free old head
        return;
    }

    // Search for the key to be deleted, keep track of the
    // previous node as we need to change 'prev->next'
    while (temp != NULL && temp->data != key) {
        prev = temp;
        temp = temp->next;
    }

    // If key was not present in linked list
    if (temp == NULL)
        return;

    // Unlink the node from linked list
    prev->next = temp->next;

    free(temp); // Free memory
}

// This function prints contents of linked list starting
// from the given node
void printList(struct Node* node)
{
    while (node != NULL) {
        printf(" %d ", node->data);
        node = node->next;
    }
}

// Driver code
int main()
{
    /* Start with the empty list */
    struct Node* head = NULL;

    push(&head, 7);
    push(&head, 1);
    push(&head, 3);
    push(&head, 2);

    puts("Created Linked List: ");
    printList(head);
    deleteNode(&head, 1);
    puts("
Linked List after Deletion of 1: ");
    printList(head);
    return 0;
}

Output:

Created Linked List: 
 2  3  1  7 
Linked List after Deletion of 1: 
 2  3  7

Time Complexity: O(n), where n represents the length of the given linked list.
Auxiliary Space: O(1), no extra space is required, so it is a constant.

Please refer complete article on Linked List | Set 3 (Deleting a node) for more details!