Reverse Words in a String II leetcode

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".

三步翻转法, 先把s = the sky is blue ---> eulb si yks eth

然后 挨个单词再翻转一遍. 

对于前面的单词碰到空格就翻转 对于最后一个单词当指针走到最后一个字符时候翻转

public class Solution {
    public void reverseWords(char[] s) {
        if (s == null || s.length == 0) {
            return;
        }
        rotate(s, 0, s.length - 1);
        int last = 0;
        for (int i = 0; i < s.length; i++) {
            if ( s[i] == ' ') {
                rotate(s, last, i - 1);
                last = i + 1;
            }
            if (i == s.length - 1) {
                rotate(s, last, i);
            }
        }
    }
    public void rotate(char[] s, int left, int right) {
        if (s == null ||s.length == 0 || left > right) {
            return;
        }
        while (left < right) {
            char tem = s[left];
            s[left] = s[right];
            s[right] = tem;
            left++;
            right--;
        }
    }
}