C Program For Swapping Nodes In A Linked List Without Swapping Data

// C program to swap the nodes of linked list
// rather than swapping the field from the nodes.
#include <stdio.h>
#include <stdlib.h>

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

/* Function to swap nodes x and y in linked list 
   by changing links */
void swapNodes(struct Node** head_ref, 
               int x, int y)
{
    // Nothing to do if x and y are same
    if (x == y)
        return;

    // Search for x (keep track of prevX and CurrX
    struct Node *prevX = NULL, *currX = *head_ref;
    while (currX && currX->data != x) 
    {
        prevX = currX;
        currX = currX->next;
    }

    // Search for y (keep track of prevY and CurrY
    struct Node *prevY = NULL, *currY = *head_ref;
    while (currY && currY->data != y) 
    {
        prevY = currY;
        currY = currY->next;
    }

    // If either x or y is not present, 
    // nothing to do
    if (currX == NULL || currY == NULL)
        return;

    // If x is not head of linked list
    if (prevX != NULL)
        prevX->next = currY;
    else 

        // Else make y as new head
        *head_ref = currY;

    // If y is not head of linked list
    if (prevY != NULL)
        prevY->next = currX;
    else 
       
        // Else make x as new head
        *head_ref = currX;

    // Swap next pointers
    struct Node* temp = currY->next;
    currY->next = currX->next;
    currX->next = temp;
}

// Function to add a node at the
// beginning of 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 of 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;
    }
}

// Driver code
int main()
{
    struct Node* start = NULL;

    // The constructed linked list is:
    // 1->2->3->4->5->6->7 
    push(&start, 7);
    push(&start, 6);
    push(&start, 5);
    push(&start, 4);
    push(&start, 3);
    push(&start, 2);
    push(&start, 1);

    printf("Linked list before calling swapNodes() ");
    printList(start);

    swapNodes(&start, 4, 3);

    printf("Linked list after calling swapNodes() ");
    printList(start);

    return 0;
}