同月生日

Same Month

个人笔记

问：一个群体中至少需要多少人，才能保证至少两个人的生日在同一个月份？

What is the minimum number of individuals required in a group to ensure that at least two share a birthday in the same month?

解析

一年有 12 个月。最坏情况下前 12 个人生日分布在 12 个不同月份。

第 13 个人无论生日在哪个月，都必与前面某人同月。

因此最少需要 13 人。

There are 12 months in a year. The worst-case top 12 birthdays are distributed over 12 different months.

The 13th person must be in the same month as someone in front of them, regardless of the month of birth.

So a minimum of 13 people is required.