題目描述：

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"

思路：

返回最後一個單詞的長度，從後遍歷整個字串，遇到空格跳出，不遇到空格，變數加1.

程式碼實現：

class Solution {
public:
    int lengthOfLastWord(string s) {
        int len=s.length();
        int i=len-1;
        int j=0;
        while(i>=0 && s[i]==' ')
        {
            i--;
        }
        while(i>=0 && s[i]!=' ')
        {
            i--;
            j++;
        }
        return j;
    }
};