189. Rotate Array

题目：

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.

[show hint]

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

链接：  http://leetcode.com/problems/rotate-array/

2/21/2017, Java

public class Solution {
    public void rotate(int[] nums, int k) {
        int rotateSize = k % nums.length;
        int[] temp = new int[rotateSize];
        int diff = nums.length - rotateSize;

        for(int i = nums.length - rotateSize; i < nums.length; i++) {
            temp[i - diff] = nums[i];
        }

        for(int i = diff - 1; i >= 0; i--) {
            nums[i + rotateSize] = nums[i];
        }

        for(int i = 0; i < rotateSize; i++) {
            nums[i] = temp[i];
        }
    }
}

别人的算法：三步反转

performance提高并不明显

public class Solution {
    public void rotate(int[] nums, int k) {
        if ((nums.length == 0) || (k % nums.length == 0)) return;
        k %= nums.length;

        reverse(nums, 0, nums.length - 1);
        reverse(nums, 0, k - 1);
        reverse(nums, k, nums.length - 1);
    }
    private void reverse(int[] nums, int lo, int hi) {
        int temp;
        while (lo < hi) {
            temp = nums[hi];
            nums[hi] = nums[lo];
            nums[lo] = temp;
            lo++;
            hi--;
        }
        return;
    }    
}