Given a string s consists of upper/lower-case alphabets and empty space characters ' ', return the length of last word in the string.
If the last word does not exist, return 0.
Note: A word is defined as a character sequence consists of non-space characters only.
For example,
Given s = "Hello World",
return 5.

考这题纯粹就是为了阴人，我确实也没想到结尾会是空格的case: "a "。

    public int lengthOfLastWord(String s) {
        if (s == null || s.length() == 0) return 0;
        //这边阴人，结尾有可能是是空格"a "
        int len = 0, tail = s.length() - 1;
        while (tail >= 0 && s.charAt(tail) == ' ')
            tail--;
        while (tail >= 0 && s.charAt(tail) != ' ') {
            len++;
            tail--;
        }
        return len;
    }

或者：

public int lengthOfLastWord(String s) {
    return s.trim().length()-s.trim().lastIndexOf(" ")-1;
}