Array Rotation in C

This program demonstrates how to rotate an array by k positions using the C programming language. The rotation is performed in-place to optimize memory usage.

Explanation of the Program

The array rotation is performed by breaking the problem into three steps:

1. Reverse the first part of the array (from index 0 to k-1).
2. Reverse the second part of the array (from index k to n-1).
3. Reverse the entire array (from index 0 to n-1).

By reversing these parts of the array, the elements are effectively rotated by k positions.

C Program

#include <stdio.h>

void reverse(int arr[], int start, int end) {
    int temp;
    while (start < end) {
        temp = arr[start];
        arr[start] = arr[end];
        arr[end] = temp;
        start++;
        end--;
    }
}

void rotateArray(int arr[], int n, int k) {
    // Handle cases where k is larger than n
    k = k % n;

    // Reverse the first part of the array
    reverse(arr, 0, k - 1);
    // Reverse the second part of the array
    reverse(arr, k, n - 1);
    // Reverse the entire array
    reverse(arr, 0, n - 1);
}

void printArray(int arr[], int n) {
    for (int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
}

int main() {
    int arr[] = {1, 2, 3, 4, 5, 6, 7};
    int n = sizeof(arr) / sizeof(arr[0]);
    int k = 3;

    printf("Original array:\n");
    printArray(arr, n);

    rotateArray(arr, n, k);

    printf("Array after rotation by %d positions:\n", k);
    printArray(arr, n);

    return 0;
}

Program Output

Original array:
1 2 3 4 5 6 7 
Array after rotation by 3 positions:
4 5 6 7 1 2 3 

Conclusion

This program effectively rotates an array by k positions using a series of three reverse operations. This approach ensures that the rotation is done in-place, optimizing memory usage while maintaining a time complexity of O(n).