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?

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public class Solution {
    public void reverseWords(char[] s) {
        if (s == null || s.length == 0) return;
        reverse(s, 0, s.length - 1);
        for (int i = 0, start = 0; i <= s.length; i++) {
            if (i == s.length || s[i] == ' ') {
                reverse(s, start, i - 1);
                start = i + 1;
            }
        }
    }
    
    public void reverse(char[] s, int start, int end) {
        if (s == null || s.length < 2 || start >= end) return;
        while (start < end) {
            char temp = s[start];
            s[start] = s[end];
            s[end] = temp;
            start++;
            end--;
        }
    }
}