# 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

Can we do this in O(1) space and in O(n) time? The following solution does.

Assuming we are given {1,2,3,4,5,6} and order 2. The basic idea is:

1. Divide the array two parts: 1,2,3,4 and 5, 6
2. Rotate first part: 4,3,2,1,5,6
3. Rotate second part: 4,3,2,1,6,5
4. Rotate the whole array: 5,6,1,2,3,4

## Code

``````public class Solution {
public void rotate(int[] nums, int k) {
int len = nums.length;
k %= len;
reverse(nums, 0, len-1);
reverse(nums, 0, k-1);
reverse(nums, k, len-1);
}

public void reverse(int[] nums, int l, int r) {
while (l <= r) {
int temp = nums[l];
nums[l] = nums[r];
nums[r] = temp;
l++;
r--;
}
}
}
``````