C Exercises: Change K^th node from beginning to end in a linked list

Last update on March 19 2025 12:36:54 (UTC/GMT +8 hours)

24. Kth Node Swapping Variants

Write a C program to swap K^th node from the beginning with K^th node from the end in a singly linked list.

Sample Solution:

C Code:

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

// Define a structure for a Node in a singly linked list
struct Node {
    int data;
    struct Node* next;
};

// Function to create a new node with given data
struct Node* new_Node(int data) {
    // Allocate memory for a new node
    struct Node* node = (struct Node*) malloc(sizeof(struct Node));
    // Set the data for the new node
    node->data = data;
    // Set the next pointer of the new node to NULL
    node->next = NULL;
    return node;
}

// Function to display the elements of a linked list
void displayList(struct Node* head) {
    while (head) {
        printf("%d ", head->data);
        head = head->next;
    }
    printf("\n");
}

// Function to swap kth node from beginning with kth node from end
void swap_Kth_Node(struct Node** head, int k) {
    if (*head == NULL) return; // If the list is empty, return

    // Count the number of nodes in the list
    int n = 0;
    struct Node *temp = *head;
    while (temp) {
        n++;
        temp = temp->next;
    }

    // Return if k is greater than the number of nodes or if k is same as the middle node
    if (k > n) return;
    if (2 * k - 1 == n) return;

    // Initialize two pointers a and b to the kth nodes from the beginning and end respectively
    struct Node *a = *head, *b = *head;
    for (int i = 1; i < k; i++)
        a = a->next;
    for (int i = 1; i < n - k + 1; i++)
        b = b->next;

    // Swap the data of nodes at positions k and n-k+1
    int t = a->data;
    a->data = b->data;
    b->data = t;
}

// Main function where the execution starts
int main() {
    // Creating a linked list
    struct Node* list = new_Node(1);
    list->next = new_Node(2);
    list->next->next = new_Node(3);
    list->next->next->next = new_Node(4);
    list->next->next->next->next = new_Node(5);

    printf("Original List: ");
    displayList(list); // Display the original list

    int k = 2;
    swap_Kth_Node(&list, k); // Swap kth node from beginning with kth node from end
    printf("\nList after swapping %dnd node from beginning and end: ", k);
    displayList(list); // Display the modified list

    k = 1;
    swap_Kth_Node(&list, k);
    printf("\nList after swapping %dst node from beginning and end: ", k);
    displayList(list);

    k = 3;
    swap_Kth_Node(&list, k);
    printf("\nList after swapping %drd node from beginning and end: ", k);
    displayList(list);

    return 0; // Indicates successful completion of the program
}

Sample Output:

Original List: 1 2 3 4 5 

List after swapping 2nd node from beginning and end: 1 4 3 2 5 

List after swapping 1st node from beginning and end: 5 4 3 2 1 

List after swapping 3rd node from beginning and end: 5 4 3 2 1

Flowchart :

For more Practice: Solve these Related Problems:

• Write a C program to swap the kth node from the beginning with the kth node from the end, handling cases where k points to the same node.
• Write a C program to swap kth nodes in a doubly linked list without swapping the data fields.
• Write a C program to recursively locate and swap kth nodes in a singly linked list by modifying pointers.
• Write a C program to swap kth nodes by rearranging node pointers instead of swapping their data, ensuring list integrity.

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