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.

Java

public class Solution {
    public int lengthOfLastWord(String s) {
        String q = s.trim();
        int c = q.length();
        int rst = 0;
        if(c == 0) {
            return rst;
        }
        do{
            rst++;
            c--;
        } while(c > 0 && q.charAt(c - 1) != ' ');
        return rst;
    }
}