C Program for array rotation?

Array rotation is a fundamental operation where elements of an array are shifted to the left or right by a specified number of positions. In left rotation, elements move left and the leftmost elements wrap around to the end.

Syntax

void leftRotate(int arr[], int n, int rotations);

Example: Left Rotation by N Positions

This program demonstrates left rotation by shifting elements one position at a time −

#include <stdio.h>

void leftRotate(int arr[], int n, int rotations) {
    int i, j, temp;
    
    for (i = 0; i < rotations; i++) {
        temp = arr[0];  // Store first element
        
        // Shift all elements one position left
        for (j = 0; j < n - 1; j++) {
            arr[j] = arr[j + 1];
        }
        
        arr[n - 1] = temp;  // Place first element at end
    }
}

int main() {
    int arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
    int n = 10;
    int rotations = 3;
    int i;
    
    printf("Original array: ");
    for (i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("
");
    
    leftRotate(arr, n, rotations);
    
    printf("After left rotation by %d: ", rotations);
    for (i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("
");
    
    return 0;
}

Original array: 1 2 3 4 5 6 7 8 9 10 
After left rotation by 3: 4 5 6 7 8 9 10 1 2 3 

Optimized Approach: Reversal Algorithm

A more efficient approach uses array reversal technique −

#include <stdio.h>

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

void leftRotateOptimized(int arr[], int n, int rotations) {
    rotations = rotations % n;  // Handle rotations greater than array size
    
    // Reverse first 'rotations' elements
    reverse(arr, 0, rotations - 1);
    
    // Reverse remaining elements
    reverse(arr, rotations, n - 1);
    
    // Reverse entire array
    reverse(arr, 0, n - 1);
}

int main() {
    int arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
    int n = 10;
    int rotations = 3;
    int i;
    
    printf("Original array: ");
    for (i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("
");
    
    leftRotateOptimized(arr, n, rotations);
    
    printf("After optimized left rotation by %d: ", rotations);
    for (i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("
");
    
    return 0;
}

Original array: 1 2 3 4 5 6 7 8 9 10 
After optimized left rotation by 3: 4 5 6 7 8 9 10 1 2 3 

Comparison

Conclusion

Array rotation can be implemented using simple shifting or the efficient reversal algorithm. The reversal method is optimal with O(n) time complexity and works well for large rotations.