How Solve places people

The rules, in the order you meet them

1. Who and what is counted. Every person on the list who has not been withdrawn, and every session of the round in the order you set. A session with capacity 0 is closed: nobody is placed in it. A ranking keeps only sessions that still exist and are open, at most the number of choices the event asks for.
2. The lottery order. Each event has a lottery number, shown as 8 characters on the Solve tab. It shuffles the list of people into one fixed order. That order only matters when two answers are equally good: then the person earlier in it is served first. New lottery changes the number and nothing else.
3. Fixed places come first. A locked place is always kept. A place you have published is kept too, unless you allow moves. Each fixed place takes one seat. If a session has more fixed places than seats, Solve stops and says so, for example "Robotics has 31 fixed places and capacity 30".
4. Rounds. With more than one round, rounds are solved in order. A session with the same title in two rounds is the same workshop, and nobody is placed in a workshop they already hold in an earlier round.
5. What counts as better. In this order: (a) more people placed; (b) then fewer people moved from a place they were told, when moves are allowed; (c) then more first choices; (d) then more second choices, and so on; (e) then fewer people in a session they did not rank. When you switch off "place people in sessions they did not rank", nobody is.
6. How it is found. Solve treats the round as a network from people to sessions, with each room's free seats as its size, and adds one person at a time along the cheapest route by the order in rule 5 (successive shortest paths). When no route is left, the result is the best possible by that order. It runs in your browser; the server checks the answer (capacities, locks, published places, each person once, real choices) before it saves it.
7. No place yet. Anyone who cannot be placed is listed as "No place yet" for you to place by hand. Placing someone by hand never publishes it by itself.
8. Re-solving. Late joiners and changed rankings of people not yet told are solved again. People already told keep their place. With moves allowed, Solve moves as few of them as it can, lists who moved, and you publish the round again to tell them.

Worked example

Sessions A (2 seats), B (1 seat) and C (1 seat). Four people, P1 to P4 in lottery order. P1 ranks A, B, C. P2 ranks A, C, B. P3 ranks A, B, C. P4 ranks B, A, C.

Result: P1 A, P2 C, P3 A, P4 B. Three first choices and one second. P1, P2 and P3 all put A first and A has 2 seats; P2 is the one given a second choice because P2's second choice (C) has room, while P3's (B) is P4's first choice.

First choice is not first come, first served

X and Y, one seat each. P1 ranks X then Y. P2 ranks only X. Solve gives X to P2 and Y to P1: 1 first choice and 1 second, rather than leaving P2 in a session they did not rank.

A lock

The first example with P4 locked to A: P4 A, P1 A, P2 C, P3 B. The lock takes one of A's seats before anyone else is placed.

After publishing

The first example is published. P5 joins late and ranks A, B, C: every seat is held by someone already told, so P5 has no place yet, and nobody moves. Raise C to 2 seats and solve again: P5 gets C and nobody else changes.

Start again from the first example, published. Raise C to 2 seats and lower A to 1. With moves off, Solve stops: "A has 2 fixed places and capacity 1". With moves allowed, it moves exactly one person: P3 goes to C, and you publish again to tell P3.

Sessions people did not rank

X and Y, one seat each, and three people who each rank only X. P1 gets X, P2 gets Y (a session P2 did not rank), and P3 has no place yet.

Limits and what is not promised

An account holds 3 events at a time, 300 people and 2 rounds in an event, with 60 sessions in a round. Solving, publishing, the fairness view, rosters and code slips are included on every account.

The fairness view reports counts: how many people got each choice, how many were placed in a session they did not rank, and how many have no place. It does not grade your sessions or your locks. Sortround follows the rule above; it does not promise that every person gets what they wanted.

Sortround is not affiliated with any event platform, school, conference or camp.