C Program For Making Middle Node Head In A Linked List

// C program to make middle node as 
// head of linked list.
#include <stdio.h>
#include <stdlib.h>

// Link list node 
struct Node 
{
    int data;
    struct Node* next;
};

/* Function to get the middle and set at
   beginning of the linked list*/
void setMiddleHead(struct Node** head)
{
    if (*head == NULL)
        return;

    // To traverse list nodes one by one
    struct Node* one_node = (*head);

    // To traverse list nodes by skipping
    // one.
    struct Node* two_node = (*head);

    // To keep track of previous of middle
    struct Node* prev = NULL;
    while (two_node != NULL && 
           two_node->next != NULL) 
    {
        // For previous node of middle node 
        prev = one_node;

        // Move one node each time
        two_node = two_node->next->next;

        // Move two node each time
        one_node = one_node->next;
    }

    // Set middle node at head 
    prev->next = prev->next->next;
    one_node->next = (*head);
    (*head) = one_node;
}

// To insert a node at the beginning 
// of linked list.
void push(struct Node** head_ref, 
          int new_data)
{
    // Allocate node 
    struct Node* new_node =
           (struct Node*)malloc(sizeof(struct Node));

    new_node->data = new_data;

    // Link the old list of the new node 
    new_node->next = (*head_ref);

    // Move the head to point to the 
    // new node 
    (*head_ref) = new_node;
}

// A  function to print a given linked list
void printList(struct Node* ptr)
{
    while (ptr != NULL) 
   {
        printf("%d ", ptr->data);
        ptr = ptr->next;
    }
    printf("");
}

// Driver code
int main()
{
    // Create a list of 5 nodes
    struct Node* head = NULL;
    int i;
    for (i = 5; i > 0; i--)
        push(&head, i);

    printf(" list before: ");
    printList(head);

    setMiddleHead(&head);

    printf(" list After:  ");
    printList(head);

    return 0;
}