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.

从后往前扫一下就可以了。注意边界

class Solution {public:    int lengthOfLastWord(string s) {        int r = s.size() - 1;        while (s[r] == ' ') r --;        r ++;        int len = r;        while (r > 0) {            if (s[-- r] == ' ') return len - r - 1;          }        return len - r;    }};