LeetCode # Array # Easy # 189. Rotate Array

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

题目：给定一个数组和一个数值k，要求将数组向右旋转k步。

以前准备面试时看到过这个题目，结果今天还是记不得空间复杂度O(1)的解法，好记性不如烂笔头。

思路：三次翻转数组，首先将整个数组逆序；然后将数组前k个逆序；最后将数组后n-k个逆序。

class Solution {
    private void reverse(int[] nums, int start, int end) {        
        while(start < end){
            int tmp = nums[start];
            nums[start] = nums[end];
            nums[end] = tmp;
            start ++;
            end --;
        }
    }
    public void rotate(int[] nums, int k) {
        int n = nums.length;
        if(n == 1){
            return;
        }
        k = k%n;
        reverse(nums, 0, n-1);
        reverse(nums, 0, k-1);
        reverse(nums, k, n-1);
    }
}

参考：https://leetcode.com/problems/rotate-array/discuss/127941/Java-1ms.-Done-In-place.-Used-reversal-algorithm.