Length of Last Word

public class Solution {
    public int lengthOfLastWord(String s) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(s == null)
            return 0;
        char[] mychar = s.trim().toCharArray();
        int count = 0;
        for(int i=0; i<mychar.length; i++)
        {
            char tmp = mychar[i];
            if(tmp == ' ')
                count = 0;
            else if((tmp >= 'A' && tmp <= 'Z')||(tmp >= 'a' && tmp <= 'z'))
                count++;
            else{
                count = 0;
                do{i++;}while(mychar[i] != ' '&&i<mychar.length);
            }
        }
        return count;
    }
}