Question

I’m working in Ruby, but I think this question is best asked agnostic of language. It may be assumed that we have access to basic list/array functions, as well as a “random” number generator. Here’s what I’d like to be able to do:

Given a collection of n teams, with n even,

1. Randomly pair each team with an opponent, such that every team is part of exactly one pair. Call this ROUND 1.
2. Randomly generate n-2 subsequent rounds (ROUND 2 through ROUND n-1) such that:
   • Each round has the same property as the first (every team is a
     member of one pair), and
   • After all the rounds, every team has faced every other team exactly once.

I imagine that algorithms for doing exactly this must be well known, but as a self-taught coder I’m having trouble figuring out how to find them.

Answer 1

I belive You are describing a round robin tournament. The wikipedia page gives an algorithm.

If You need a way to randomize the schedule, randomize team order, round order, etc.