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.

思路：从尾部向前遍历，找到第一个为空格的字符，这个就是最后一个单词的长度

#include <iostream>
#include <string>
#include <vector>
using namespace std;

int LengthofLastWord(string& str)
{
	if(str.length() == 0)
		return 0;
	int len=0,i=str.length()-1;
	for(;i>=0;i--)
		if(str[i] ==‘ ‘)
			break;
		else
			len++;
	return len;
} 

int main()
{
	string str("Hello world");
	cout<<LengthofLastWord(str)<<endl;
	return 0;
}