C Program to Move the Last Node to the Front of a Linked List

Here we’ll see how to write C Program to move the last node to the front of a linked list. We can do that just by re-arranging the pointers. No need to create or delete any node.

Logic to Move the Last Node to the Front

1. If the linked list is empty or has only one element, then return. If the list has only one element, then the first node and the last node are basically same.
2. Point prev to the first node and cur to the second node.
3. Keep moving both prev and cur to the next nodes until cur->next becomes NULL. cur->next pointing to NULL means cur pointing to the last node and prev pointing to the second last node.
4. Point the second last node to NULL (prev->next = NULL), last node to the first node (cur->next = head). And assign head where cur is pointing to (head = cur).

The Program

/*File: test.c*/

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

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

/*Move the last node to the front.*/
void move_last_node_to_front(struct node **head) {
  struct node *prev = NULL, *cur = NULL;

  /*Return if there is no node or only one node*/
  if(head == NULL || *head == NULL || (*head)->next == NULL) return;
  
  prev = *head;
  cur = prev->next;
  
  /*Going to the last node*/
  while(cur->next) {
    prev = prev->next;
    cur = cur->next;
  }
  
  prev->next = NULL;
  cur->next = *head;
  *head = cur;
}

/*Print the linked list*/
void print_list(struct node *head) {
    
    printf("H->");

    while(head)
    {
        printf("%d->", head->val);
        head = head->next;
    }

    printf("|||\n");
}

/*Insert an element at the front of the list*/
void insert_front(struct node **head, int value) {
    
    struct node * new_node = NULL;

    /*Allocating memory for the new node*/
    new_node = (struct node *)malloc(sizeof(struct node));

    if (new_node == NULL)
    {
        printf("Failed to insert element. Out of memory");
    }

    new_node->val = value;

    /*Pointing the new node to where head is currently pointing to*/
    new_node->next = *head;

    /*Pointing head to new node.*/
    *head = new_node;
}

void main()
{
    int count = 0, i, val;
    struct node * head = NULL;

    printf("Enter number of elements: ");
    scanf("%d", &count);

    for (i = 0; i < count; i++)
    {
        printf("Enter %dth element: ", i);
        scanf("%d", &val);
        insert_front(&head, val);
    }

    printf("Initial Linked List: ");
    print_list(head);
    
    move_last_node_to_front(&head);
    
    printf("Linked List after movinf last node to front: ");
    print_list(head);
}

This program first takes input of some numbers to create the linked list. Then it calls the move_last_node_to_front() function to move the last node to the front.

Here is the output.

From the output we can see that initially 43 was the last node. After the move_last_node_to_front() function call, it became the first node of the linked list.

Read also: Insert an element to a linked list.

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