If you do a simple google search or look through one of several lists of swiss tournament scheduling programs out there, you'll find that there is no shortage in this arena due to the abundance of chess, go, and card tournaments using this format. Swiss scheduling is clearly a difficult problem and is one that a lot of people attempt to build programs for. My first instinct was thus to use an existing program and just manually add a bunch of games to Leaguevine each round during the tournament. Yeah, I know, keeping track of games on both Leaguevine and an external scheduler sounds awful. What makes this approach even worse is that after looking into these existing programs, they tended to do a very poor job of scheduling because they did not ensure that there were no rematches.
Thus, we built our own.
- No team should play another team more than once during the tournament
- No team should have more than one bye during the tournament
Because of this, the matchups that are generated by a tournament scheduler using any of the group pairing techniques will result in matchups that violate either of these two constraints. Almost every piece of existing software I've seen simply points out which ones violate the constraints, but leave it entirely up to the tournament director to resolve the problems. There does appear to be one program out there that resolves these conflicts, but I didn't notice it until well after I finished coding the algorithm up. Luckily it only took a couple days!I've seen many articles explaining how to resolve any conflicts with these constraints. They tend to list a sequence of steps for either changing the matchups until you find something that works or reordering the standings until you find something that works. However, at the end of these steps usually comes a line that says "this approach usually works but doesn't work all of the time.". Another problem I see with these approaches is that it is very difficult for a person to manually change a matchup and have that change be the optimal possible change. There is just too much room for error.