189. Rotate Array

Rotate an array of n elements to the right by k steps.

For example, with n = 7 and k = 3, the array [1,2,3,4,5,6,7] is rotated to [5,6,7,1,2,3,4]. 

Note:
Try to come up as many solutions as you can, there are at least 3 different ways to solve this problem.

Hint:

Could you do it in-place with O(1) extra space?

Related problem: Reverse Words in a String II

Solution:

1. Reverse the entire input array.

2. Reverse from 0 to k - 1.

2. Reverse from k to the end.



Code:

public class Solution {
    public void rotate(int[] nums, int k) {
        k = k % nums.length;
        reverse(nums, 0, nums.length - 1);
        reverse(nums, 0, k - 1);
        reverse(nums, k, nums.length - 1);
    }
    
    public void reverse(int[] nums, int i, int j) {
        while (i < j) {
            int swap = nums[i];
            nums[i++] = nums[j];
            nums[j--] = swap;
        }
    }
}