# HackerRank Solutions – Arrays – Left Rotation – Java Solution

All credits to Rodney Shaghoulian for this simple solution for the HackerRank challenge – Arrays – Left Rotation. This solution is written in Java.

// Author: Rodney Shaghoulian
// Github: github.com/RodneyShag

import java.util.Scanner;

//  Time Complexity: O(n)
// Space Complexity: O(1) by doing an "in place" rotation
public class Solution {
public static void main(String[] args) {
/* Save input */
Scanner scan = new Scanner(System.in);
int size         = scan.nextInt();
int numRotations = scan.nextInt();
int array[] = new int[size];
for (int i = 0; i < size; i++) {
array[i] = scan.nextInt();
}
scan.close();

/* Rotate array (in place) using 3 reverse operations */
numRotations %= size; // to account for numRotations > size
int rotationSpot = size - 1 - numRotations;
reverse(array, 0, size - 1);
reverse(array, 0, rotationSpot);
reverse(array, rotationSpot + 1, size - 1);

/* Print rotated array */
for (int i = 0; i < size; i++) {
System.out.print(array[i] + " ");
}
}

/* Reverses array from "start" to "end" inclusive */
private static void reverse(int[] array, int start, int end) {
if (array == null || start < 0 || start >= array.length || end < 0 || end >= array.length) {
return;
}
while (start < end) {
swap(array, start++, end--);
}
}

private static void swap(int [] array, int i, int j) {
int temp = array[i];
array[i] = array[j];
array[j] = temp;
}
}