Linked List | Set 3 (Deleting a node)

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. 
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.

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("\nLinked 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