Wednesday, 19 October 2016

Delete a Linked List node at a given position

Delete a Linked List node at a given position

Given a singly linked list and a position, delete a linked list node at the given position.
Example:
Input: position = 1, Linked List = 8->2->3->1->7
Output: Linked List =  8->3->1->7

Input: position = 0, Linked List = 8->2->3->1->7
Output: Linked List = 2->3->1->7
We strongly recommend you to minimize your browser and try this yourself first
If node to be deleted is root, simply delete it. To delete a middle node, we must have pointer to the node previous to the node to be deleted. So if positions is not zero, we run a loop position-1 times and get pointer to the previous node.
Below is C implementation of above idea.
// A complete working C program to delete a node in a linked list
// at a given position
#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 position, deletes the node at the given position */
void deleteNode(struct node **head_ref, int position)
{
   // If linked list is empty
   if (*head_ref == NULL)
      return;
 
   // Store head node
   struct node* temp = *head_ref;
 
    // If head needs to be removed
    if (position == 0)
    {
        *head_ref = temp->next;   // Change head
        free(temp);               // free old head
        return;
    }
 
    // Find previous node of the node to be deleted
    for (int i=0; temp!=NULL && i<position-1; i++)
         temp = temp->next;
 
    // If position is more than number of ndoes
    if (temp == NULL || temp->next == NULL)
         return;
 
    // Node temp->next is the node to be deleted
    // Store pointer to the next of node to be deleted
    struct node *next = temp->next->next;
 
    // Unlink the node from linked list
    free(temp->next);  // Free memory
 
    temp->next = next;  // Unlink the deleted node from list
}
 
// 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;
    }
}
 
/* Drier program to test above functions*/
int main()
{
    /* Start with the empty list */
    struct node* head = NULL;
 
    push(&head, 7);
    push(&head, 1);
    push(&head, 3);
    push(&head, 2);
    push(&head, 8);
 
    puts("Created Linked List: ");
    printList(head);
    deleteNode(&head, 4);
    puts("\nLinked List after Deletion at position 4: ");
    printList(head);
    return 0;
}

Output:
Created Linked List: 
 8  2  3  1  7 
Linked List after Deletion at position 4: 
 8  2  3  1 
Thanks to Hemanth Kumar for suggesting initial solution. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

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