> 各位计算机的高手们:
>     你们好!
>     在下最近碰到了一到很难的题(当然了，是相对于我这个小菜鸟而言 的),题目是这样的:
> Sum
> 
> Mr. Jojer is given n numbers and an extra integer x, he wants to know whether there are two numbers whose sum is x. 
> 
> 
> Input
> 
> The input file contains several test cases. The first line of each test case contains two integers, n(<=1000001) and x. From the next line of each test case, there are n numbers. 
> 
> 
> Output
> 
> Each test case corresponds to a line in the output, which is either "YES" if there exists an answer or "NO" if not. 
> 
> 
> Sample Input 
> 
> 
> 3 3
> 1 2 3
> 2 3
> 1 3
> 
> 
> 
> 
> Sample Output 
> 
> YES
> NO
> 
> 
> 题目来自于四川安心在线评判(网址:http://acm.scu.edu.cn/online_judge/problem.do?problem=1627),希望哪位好心人能帮帮我啊,在下不胜感激