Reverse Words in a String II

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 itin-placewithout allocating extra space?

Tips:

先颠倒整个数列，然后再逐词颠倒。注意判断条件r < s.length。

Code:

public class Solution {
    public void reverseWords(char[] s) {
        if (s == null || s.length == 0) return;
        reverse(s, 0, s.length - 1);
        int l = 0, r = 0;
        while (r < s.length) {
            l = r;
            while (r < s.length && s[r] != ' ') {
                r++;
            }
            reverse(s, l, r - 1);
            r++;
        }
    }

    private void reverse(char[] s, int start, int end) {
        while (start < end) {
            char temp = s[start];
            s[start] = s[end];
            s[end] = temp;
            start++;
            end--;
        }
    }
}