public String reverseWords_lint(String s) {
        if (s == null || s.length() == 0)
            return s;
        StringBuilder sb = new StringBuilder();
        String [] arr = s.trim().split("\\s+");
        for (int i = arr.length - 1; i > 0; --i) {
            sb.append(arr[i] + " ");
        }
        sb.append(arr[0]);
        return sb.toString();
    }