Length of Last Word

Problem:

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.

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