Example: Left Array Rotation One-by-One in Java

// Left Array Rotation One-by-One
import java.util.Arrays;

// Main class containing the entry point of the program
public class Main {
    /**
     * Performs a single left rotation on the array.
     * The first element moves to the end, and all others shift left.
     *
     * @param arr The array to be rotated.
     */
    static void rotateOneElementLeft(int[] arr) {
        // Handle edge cases: null array or array with 0 or 1 element
        if (arr == null || arr.length <= 1) {
            return;
        }
        int first = arr[0]; // Step 1: Store the first element
        // Step 2: Shift remaining elements to the left by one position
        for (int i = 0; i < arr.length - 1; i++) {
            arr[i] = arr[i + 1];
        }
        arr[arr.length - 1] = first; // Step 3: Place the stored first element at the end
    }

    /**
     * Performs 'd' left rotations on an array using the one-by-one method.
     *
     * @param arr The array to be rotated.
     * @param d The number of positions to rotate left.
     */
    static void leftRotateOneByOne(int[] arr, int d) {
        if (arr == null || arr.length == 0) {
            return;
        }
        // Adjust d
        d = d % arr.length;
        for (int i = 0; i < d; i++) {
            rotateOneElementLeft(arr); // Rotate by one element, d times
        }
    }

    public static void main(String[] args) {
        // Example 1
        int[] arr1 = {1, 2, 3, 4, 5};
        int d1 = 2; // Number of positions to rotate left

        System.out.println("Original Array: " + Arrays.toString(arr1));
        leftRotateOneByOne(arr1, d1);
        System.out.println("Array after " + d1 + " left rotations (one-by-one): " + Arrays.toString(arr1));

        System.out.println("-------------------------------------");

        // Example 2
        int[] arr2 = {100, 200, 300, 400, 500, 600};
        int d2 = 4;
        System.out.println("Original Array: " + Arrays.toString(arr2));
        leftRotateOneByOne(arr2, d2);
        System.out.println("Array after " + d2 + " left rotations (one-by-one): " + Arrays.toString(arr2));
    }
}