Java - Rotating array

Question

So the goal is to rotate the elements in an array right a times. As an example; if a==2, then array = {0,1,2,3,4} would become

Answer 1

Java solution wrapped in a method:

public static int[] rotate(final int[] array, final int rIndex) {
    if (array == null || array.length <= 1) {
        return new int[0];
    }

    final int[] result = new int[array.length];
    final int arrayLength = array.length;

    for (int i = 0; i < arrayLength; i++) {
        int nIndex = (i + rIndex) % arrayLength;
        result[nIndex] = array[i];
    }
    return result;
}

Answer 2

Question : https://www.hackerrank.com/challenges/ctci-array-left-rotation
Solution : This is how I tried arrayLeftRotation method with complexity o(n)

• looping once from k index to (length-1 )

• 2nd time for 0 to kth index

  public static int[] arrayLeftRotation(int[] a, int n, int k) {
  int[] resultArray = new int[n];
  int arrayIndex = 0;
  //first n-k indexes will be populated in this loop
  for(int i = k ; i resultArray[arrayIndex] = a[i];
  arrayIndex++;
  }
  // 2nd k indexes will be populated in this loop
  for(int j=arrayIndex ; j<(arrayIndex+k); j++){
  resultArray[j]=a[j-(n-k)];
  }
  return resultArray;
  }

Answer 3

package com.array.orderstatistics;

import java.util.Scanner;

public class ArrayRotation {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int r = scan.nextInt();
        int[] a = new int[n];
        int[] b = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = scan.nextInt();
        }
        scan.close();

        if (r % n == 0) {
            printOriginalArray(a);
        } else {
            r = r % n;
            for (int i = 0; i < n; i++) {
                b[i] = a[(i + r) < n ? (i + r) : ((i + r) - n)];
                System.out.print(b[i] + " ");
            }
        }
    }

    private static void printOriginalArray(int[] a) {
        for (int i = 0; i < a.length; i++) {
            System.out.print(a[i] + " ");
        }
    }

}

Answer 4

For Left Rotate its very simple

Take the difference between length of the array and number of position to shift.

For Example

int k = 2;
int n = 5;

int diff = n - k;

int[] array = {1, 2, 3, 4, 5};
int[] result = new int[array.length];
System.arraycopy(array, 0, result, diff, k);
System.arraycopy(array, k, result, 0, diff);

// print the output

Answer 5

In ruby rotating an array can be possible in one line.

def array_rotate(arr)
   i, j = arr.length - 1, 0
   arr[j],arr[i], i, j = arr[i], arr[j], i - 1, j + 1 while(j<arr.length/2)
   puts "#{arr}"
end

Answer 6

Another way is copying with System.arraycopy.

    int[] temp = new int[array.length];
    System.arraycopy(array, 0, temp, a, array.length - a);
    System.arraycopy(array, array.length-a, temp, 0, a);