leetcode 186. Reverse Words in a String II 旋转字符数组 ---------- java

Given an input string, reverse the string word by word. A word is defined as a sequence of non-space characters.

The input string does not contain leading or trailing spaces and the words are always separated by a single space.

For example,
Given s = "the sky is blue",
return "blue is sky the".

Could you do it in-place without allocating extra space?

1、刚开始的想法是找到第一个和最后一个单词，然后交换他们两个，但是遇到的问题是两个单词长度不一致的时候会很麻烦，就需要将剩余的字符串整个进行移动，麻烦，且效率很低。

2、参考了discuss，发现很其实想法很简单，就是分两步：第一步就是把整个字符串倒过来，第二步就是再翻回来之后再把每个单词反转一次就好了。

public class Solution {
    public void reverseWords(char[] s) {
        int len = s.length;
        reverse(s, 0, len - 1);
        int start = 0;
        for (int i = 0; i < len - 1; i++){
            if (s[i] == ' '){
                reverse(s, start, i - 1);
                start = i + 1;
            }
        }
        reverse(s, start, len - 1);
    }
    private void reverse(char[] s, int start, int end){
        while (start < end){
            char ch = s[start];
            s[start] = s[end];
            s[end] = ch;
            start++;
            end--;
        }
    }
}