握手数必有相同
Handshakes
题目详情
你在一个聚会中，除你之外还有 25 个队友，每个队友都与你握过手，队友之间可能也互相握手。
能否断言：一定至少有两个人握手次数相同？
You are at a party with 25 team members, each of whom shakes your hand. There might be additional handshakes among others. Can you say with certainty there are at least two people with the same number of handshakes?
解析
可以。
共有 26 人。由于每个队友都与你握过手，因此队友的握手次数至少为 1、至多为 25。
握手次数可能取值只有 25 种（1..25），但有 26 个人（包括你也在内会产生同样结论），由抽屉原理，至少两个人握手次数相同。
Original Explanation
Yes. There are 26 people total (you + 25). Possible handshake counts range from 0 to 25, but you already shook hands with each team member, so their handshake counts range from 1 to 25. That is 25 possible handshake counts for 26 people, so by the pigeonhole principle, at least two people must have the same count.