1.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.

Example:
Input: "Hello World"
Output: 5

2.题目要求：给定一个字符串，然后判断最后一个单词的长度。

3.方法：要记录的是空格前的字符开始索引，然后遇到空格得出单词长度。最后要注意的是，可能整个字符没有空格，或者最后一个不是空格，退出循环时要检测一下。

4.代码：
class Solution {
public:
int lengthOfLastWord(string s) {
int len = 0, tail = s.length() - 1;
while (tail >= 0 && s[tail] == ' ') tail--;
while (tail >= 0 && s[tail] != ' ') {
len++;
tail--;
}
return len;
}
};