Deleting a node in linked list

Delete a given node from the linked list.

Example

Linked List : 10 20 30 NULL

Input

Output

10 30 NULL

Input

Output

10 20 NULL

Algorithm

1. If the head node has the given key,

make the head node points to the second node and free its memory.

2. Otherwise,

From the current node, check whether the next node has the given key

if yes, make the current->next = current->next->next and free the memory.

else, update the current node to the next and do the above process (from step 2) till the last node.

1. Head node has the given key

void deleteNode(struct node **head, int key)
{
      //temp is used to freeing the memory
      struct node *temp;
     
      //key found on the head node.
      //move to head node to the next and free the head.
      if(*head->data == key)
      {
          temp = *head;    //backup the head to free its memory
          *head = (*head)->next;
          free(temp);
      }
    
}

Visual Representation

Let's delete data 10 (head node).

1. Make the head points to the next node.

2. Free the head node's memory.

3. Finally, the new linked list.

2. For other nodes (Non-Head)

void deleteNode(struct node **head, int key)
{
      //temp is used to freeing the memory
      struct node *temp;

      //key found on the head node.
      //move to head node to the next and free the head.
      if((*head)->data == key)
      {
          temp = *head;    //backup to free the memory
          *head = (*head)->next;
          free(temp);
      }
      
      else
      {
          struct node *current  = *head;
          while(current->next != NULL)
          {
              //if yes, we need to delete the current->next node
              if(current->next->data == key)
              {
                  temp = current->next;
                  //node will be disconnected from the linked list.
                  current->next = current->next->next;
                  free(temp);
                  break;
              }
              //Otherwise, move the current node and proceed
              else
                  current = current->next;
          }
      }
    
}

Visual Representation

Let's delete data 20.

1. Make the current node points to the head node. (current => data = 10).

2. current => next. (current=>next=>data = 20).

3. current => next => next. (current=>next=>next=>data = 30).

4. We have to remove the node 20. Since current => next = 20 we can remove the node by setting current => next = current =>next => next. And then free the node.

5. Finally, the new linked list.

Implementation of deleting a node in linked list

Example

/*
 * Program: Deleting a node in the linked list
 * Language: C
 */

#include<stdio.h>
#include<stdlib.h>

struct node
{
    int data;
    struct node *next;
};

void addLast(struct node **head, int val)
{
    //create a new node
    struct node *newNode = malloc(sizeof(struct node));
    newNode->data = val;
    newNode->next     = NULL;

    //if head is NULL, it is an empty list
    if(*head == NULL)
         *head = newNode;
    //Otherwise, find the last node and add the newNode
    else
    {
        struct node *lastNode = *head;

        //last node's next address will be NULL.
        while(lastNode->next != NULL)
        {
            lastNode = lastNode->next;
        }

        //add the newNode at the end of the linked list
        lastNode->next = newNode;
    }

}

void deleteNode(struct node **head, int key)
{
      //temp is used to freeing the memory
      struct node *temp;

      //key found on the head node.
      //move to head node to the next and free the head.
      if((*head)->data == key)
      {
          temp = *head;    //backup to free the memory
          *head = (*head)->next;
          free(temp);
      }
      else
      {
          struct node *current  = *head;
          while(current->next != NULL)
          {
              //if yes, we need to delete the current->next node
              if(current->next->data == key)
              {
                  temp = current->next;
                  //node will be disconnected from the linked list.
                  current->next = current->next->next;
                  free(temp);
                  break;
              }
              //Otherwise, move the current node and proceed
              else
                  current = current->next;
          }
      }
}

void printList(struct node *head)
{
    struct node *temp = head;

    //iterate the entire linked list and print the data
    while(temp != NULL)
    {
         printf("%d ->", temp->data);
         temp = temp->next;
    }
    printf("NULL\n");
}

int main()
{
     struct node *head = NULL;

     addLast(&head,10);
     addLast(&head,20);
     addLast(&head,30);
     printf("Linked List Elements:\n");
     printList(head);

     //delete first node
     deleteNode(&head,10);
     printf("Deleted 10. The New Linked List:\n");
     printList(head);

     //delete last node
     deleteNode(&head,30);
     printf("Deleted 30. The New Linked List:\n");
     printList(head);

     //delete 20
     deleteNode(&head,20);
     printf("Deleted 20. The New Linked List:\n");
     printList(head);

     return 0;
}