# Question

Formatted question description: https://leetcode.ca/all/189.html

 189. Rotate Array

Given an array, rotate the array to the right by k steps, where k is non-negative.

Example 1:

Input: [1,2,3,4,5,6,7] and k = 3
Output: [5,6,7,1,2,3,4]
Explanation:
rotate 1 steps to the right: [7,1,2,3,4,5,6]
rotate 2 steps to the right: [6,7,1,2,3,4,5]
rotate 3 steps to the right: [5,6,7,1,2,3,4]

Example 2:

Input: [-1,-100,3,99] and k = 2
Output: [3,99,-1,-100]
Explanation:
rotate 1 steps to the right: [99,-1,-100,3]
rotate 2 steps to the right: [3,99,-1,-100]

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

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

@tag-array



# Algorithm

O(1) extra space.

Similar to the method of flipping characters, the idea is to flip the first n-k numbers first, then flip the last k numbers, and finally flip the entire array.

[1,2,3,4,5,6,7] => [4,3,2,1,5,6,7]

[4,3,2,1,5,6,7] => [4,3,2,1,7,6,5]

[4,3,2,1,7,6,5] => [5,6,7,1,2,3,4]


Java