LeetCode: Reverse Words in a String II

/**
 * Description: Given an input string, reverse the string word by word. A word is defined as a sequence of non-space
 * characters.
 * <p/>
 * The input string does not contain leading or trailing spaces and the words are always separated by a single space.
 * <p/>
 * For example, Given s = "the sky is blue", return "blue is sky the".
 * <p/>
 * Could you do it in-place without allocating extra space?
 *
 * @author hzhou
 */
public class ReverseWordsInAStringII {
    public void reverseWords(char[] s) {
        if (s == null || s.length == 0) {
            return;
        }
        arrayReverse(s, 0, s.length - 1);
        for (int i = 0; i < s.length - 1; ) {
            int j = i + 1;
            while (j < s.length && s[j] != ' ') {
                j++;
            }
            arrayReverse(s, i, j - 1);
            i = j + 1;
        }
    }
    private void arrayReverse(char[] s, int start, int end) {
        if (s == null || s.length == 0 || start >= end) {
            return;
        }
        char tmp;
        for (int i = start; i <= (end + start) / 2; i++) {
            tmp = s[i];
            s[i] = s[end + start - i];
            s[end + start - i] = tmp;
        }
    }
    @Test
    public void test() {
        char[] s = new char[]{'a', 'f', ' ', 'g'};
        reverseWords(s);
    }
}