Extremely simple one, but my favorite is an algorithm for determining if two words are anagrams of each other:
The Fundamental Theorem of Arithmetic states: "every integer greater than 1 either is a prime number itself or can be represented as the product of prime numbers and that, moreover, this representation is unique, up to (except for) the order of the factors."[1]
So to determine that two words are anagrams of each other, you can assign each letter to a unique prime number (a = 2, b = 3, c = 5 etc.), then compute the product of those numbers, and if they're equal then those two words are anagrams.
The Fundamental Theorem of Arithmetic states: "every integer greater than 1 either is a prime number itself or can be represented as the product of prime numbers and that, moreover, this representation is unique, up to (except for) the order of the factors."[1]
So to determine that two words are anagrams of each other, you can assign each letter to a unique prime number (a = 2, b = 3, c = 5 etc.), then compute the product of those numbers, and if they're equal then those two words are anagrams.
[1] - https://en.wikipedia.org/wiki/Fundamental_theorem_of_arithme...