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

Arraycopy is an expensive operation, both time and memory wise. Following would be an efficient way to rotate array without using extra space (unlike the accepted answer where a new array is created of the same size).

public void rotate(int[] nums, int k) { // k = 2
    k %= nums.length;
    // {0,1,2,3,4}

    reverse(nums, 0, nums.length - 1); // Reverse the whole Array
    // {4,3,2,1,0}

    reverse(nums, 0, k - 1); // Reverse first part (4,3 -> 3,4)
    // {3,4,2,1,0}

    reverse(nums, k, nums.length - 1); //Reverse second part (2,1,0 -> 0,1,2)
    // {3,4,0,1,2}
}

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

Answer 2

Add a modulo array length to your code:

// create a newArray before of the same size as array

// copy
for(int x = 0; x <= array.length-1; x++){
  newArray[(x+a) % array.length ] = array[x];
}

You should also create a new Array to copy to, so you do not overwrite values, that you'll need later on.