原题链接在这里：https://leetcode.com/problems/length-of-last-word/

题目：

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.

题解：

从最后一个char 开始往前扫，遇到第一个空格就时就走完了最后一个词。

不过要注意最后一个char 本身就是空格的情况，所以需要先把s trim()一下。

Time Complexity: O(s.length()).

Space: O(1).

AC Java:

 1 public class Solution {
 2     public int lengthOfLastWord(String s) {
 3         if(s == null || s.length() == 0){
 4             return 0;
 5         }
 6         
 7         s = s.trim();
 8         int i = s.length()-1;
 9         while(i>=0){
10             if(s.charAt(i) == ' '){
11                 break;
12             }else{
13                 i--;
14             }
15         }
16         return s.length()-1-i;
17     }
18 }