C Exercises: Rotate a singly linked list to the right by k places

C Singly Linked List : Exercise-23 with Solution

Write a C program that rotates a singly linked list to the right by k places.

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* newNode(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 rotate a linked list by a given number of positions
void rotate_List(struct Node** head_ref, int k) {
    struct Node* current = *head_ref;
    int count = 1;

    // Find the last node of the linked list and count the total nodes
    while (current->next) {
        current = current->next;
        count++;
    }

    // Set the next of the last node to the head, making it circular
    current->next = *head_ref;

    // Find the (count - k % count)th node from the beginning
    for (int i = 0; i < count - k % count; i++) {
        current = current->next;
    }

    // Set the (count - k % count)th node as the new head and break the link to form a new tail
    *head_ref = current->next;
    current->next = NULL;
}

// Main function where the execution starts
int main() {
    // Creating a linked list
    struct Node* list1 = newNode(1);
    list1->next = newNode(3);
    list1->next->next = newNode(4);
    list1->next->next->next = newNode(7);   
    list1->next->next->next->next = newNode(9);

    printf("Original List: ");
    displayList(list1); // Display the original list

    int k = 1;
    printf("\nRotate the said singly linked list to the right by %d places:\n", k);
    rotate_List(&list1, k); // Rotate the list by k places to the right
    displayList(list1); // Display the rotated list

    k = 2;
    printf("\nRotate the said singly linked list to the right by %d places:\n", k);
    rotate_List(&list1, k); // Rotate the list by k places to the right
    displayList(list1); // Display the rotated list

    k = 4;
    printf("\nRotate the said singly linked list to the right by %d places:\n", k);
    rotate_List(&list1, k); // Rotate the list by k places to the right
    displayList(list1); // Display the rotated list

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

Sample Output:

Original List: 1 3 4 7 9 

Rotate the said singly linked list to the right by 1 places:
9 1 3 4 7 

Rotate the said singly linked list to the right by 2 places:
4 7 9 1 3 

Rotate the said singly linked list to the right by 4 places:
7 9 1 3 4 

Flowchart :

C Programming Code Editor:

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