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.

題意，找到，最后一個' '后面的單詞，求出它的長度，如果沒有，就返回0。

思路：從后向前遍歷，發現是字母了，觸發標識位，如果還是字母繼續，發現' '直接停止，返回剛才的單詞的長度。

java代碼：

public int lengthOfLastWord(String s) { 
        if(s==null || s.length() == 0)
            return 0;
     
        int result = 0;
        int len = s.length();
     
        boolean flag = false;
        for(int i=len-1; i>=0; i--){
            char c = s.charAt(i);
            if((c>='a' && c<='z') || (c>='A' && c<='Z')){
                flag = true;
                result++;
            }else{
                if(flag)
                    return result;
            }
        }
     
        return result;
    }