注意这种第一个不符合要求的元素的求法的写法

class Solution {
    public int lengthOfLastWord(String s) {
        if(s==null||s.length()==0) return 0;
        int pos = s.length()-1;
        int result = 0;
        while(pos>=0&&s.charAt(pos)==' ')
                pos--;
           // last not null character
        if(pos==-1)
        return 0;
        // do not have any content
         int end =pos;
         while(pos>=0&&s.charAt(pos)!=' ')
                pos--;
            int start=pos;
         return end-start;       
       }
}