func reverseWords(s string) string {
    length := len(s)
    ret := []byte{}
    for i := 0; i < length; {
        start := i
        for i < length && s[i] != ' ' {
            i++
        }
        for p := start; p < i; p++ {
            ret = append(ret, s[start + i - 1 - p])
        }
        for i < length && s[i] == ' ' {
            i++
            ret = append(ret, ' ')
        }
    }
    return string(ret)
}