C Program For Deleting A Linked List Node At A Given Position (original) (raw)

Last Updated : 16 Jun, 2022

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

If the node to be deleted is the root, simply delete it. To delete a middle node, we must have a pointer to the node previous to the node to be deleted. So if positions are not zero, we run a loop position-1 times and get a pointer to the previous node.

Below is the implementation of the above idea.

C `

// 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 nodes
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; } }

/* Driver 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("

Linked 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

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 Delete a Linked List node at a given position for more details!