C Program To Delete Alternate Nodes Of A Linked List
Given a Singly Linked List, starting from the second node delete all alternate nodes of it. For example, if the given linked list is 1->2->3->4->5 then your function should convert it to 1->3->5, and if the given linked list is 1->2->3->4 then convert it to 1->3.
Method 1 (Iterative):
Keep track of previous of the node to be deleted. First, change the next link of the previous node and iteratively move to the next node.
C
#include<stdio.h>
#include<stdlib.h>
struct Node
{
int data;
struct Node *next;
};
void deleteAlt( struct Node *head)
{
if (head == NULL)
return ;
struct Node *prev = head;
struct Node *node = head->next;
while (prev != NULL &&
node != NULL)
{
prev->next = node->next;
free (node);
prev = prev->next;
if (prev != NULL)
node = prev->next;
}
}
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;
}
void printList( struct Node *node)
{
while (node != NULL)
{
printf ( "%d " , node->data);
node = node->next;
}
}
int main()
{
struct Node* head = NULL;
push(&head, 5);
push(&head, 4);
push(&head, 3);
push(&head, 2);
push(&head, 1);
printf ( "\nList before calling deleteAlt() \n" );
printList(head);
deleteAlt(head);
printf ( "\nList after calling deleteAlt() \n" );
printList(head);
return 0;
}
|
Output:
List before calling deleteAlt()
1 2 3 4 5
List after calling deleteAlt()
1 3 5
Time Complexity: O(n) where n is the number of nodes in the given Linked List.
Auxiliary Space: O(1) because it is using constant space
Method 2 (Recursive):
Recursive code uses the same approach as method 1. The recursive code is simple and short but causes O(n) recursive function calls for a linked list of size n.
C
void deleteAlt( struct Node *head)
{
if (head == NULL)
return ;
struct Node *node = head->next;
if (node == NULL)
return ;
head->next = node->next;
free (node);
deleteAlt(head->next);
}
|
Time Complexity: O(n)
Auxiliary space: O(n) for call stack because using recursion
Please refer complete article on Delete alternate nodes of a Linked List for more details!
Last Updated :
28 Mar, 2023
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