58. Length of Last Word

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;
    }
};