In either case, I take that value and multiply back by two, if it was even I get back the original number, if it was odd, I'm not going to get back the original number, so I can just check to see if they're the same.

在两种情况中，我都把结果值,再乘以2，如果x是偶数我就,得到了原来的值，如果x是奇数那么就不会得到,原来的值，因此我看看得到的值,和原来的值相等不相等就可以了。

麻省理工公开课 - 计算机科学及编程导论课程节选