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.
// C program to remove alternate nodes of a linked list
#include<stdio.h>
#include<stdlib.h>
/* A linked list node */
struct Node
{
int data;
struct Node *next;
};
/* deletes alternate nodes of a list starting with head */
void deleteAlt(struct Node *head)
{
if (head == NULL)
return;
/* Initialize prev and node to be deleted */
struct Node *prev = head;
struct Node *node = head->next;
while (prev != NULL && node != NULL)
{
/* Change next link of previous node */
prev->next = node->next;
/* Free memory */
free(node);
/* Update prev and node */
prev = prev->next;
if (prev != NULL)
node = prev->next;
}
}
/* UTILITY FUNCTIONS TO TEST fun1() and fun2() */
/* Given a reference (pointer to pointer) to the head
of a list and an int, push a new node on the front
of the list. */
void push(struct Node** head_ref, int new_data)
{
/* allocate node */
struct Node* new_node =
(struct Node*) malloc(sizeof(struct Node));
/* put in the data */
new_node->data = new_data;
/* link the old list off the new node */
new_node->next = (*head_ref);
/* move the head to point to the new node */
(*head_ref) = new_node;
}
/* Function to print nodes in a given linked list */
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;
/* Using push() to construct below list
1->2->3->4->5 */
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
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