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 it in-place without allocating extra space?

Do it in place: reverse the whole string. For each subarray separated by ' ', reverse the subarray.

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