Pigeonhole Principle

If you have $n$ pigeons and $k$ holes such that $n > k$. 1 hole will have more than 1 pigeon.

Application
https://leetcode.com/problems/contains-duplicate/description/

Example

Input: nums = [1,2,3,1]
Output: true

def containsuplicate(nums: List[int]) -> bool:
	return len(set(nums)) < len(nums)