Dots and Boxes

A two-player game of edges and territory. Players take turns drawing one edge between adjacent dots. Closing the fourth side of a box claims it and earns another move. When every edge is drawn, the player who claimed more boxes wins.

Board

A grid of 5 x 5 boxes, so 6 x 6 dots. There are 60 edges in total (30 horizontal, 30 vertical) and 25 boxes. The box count is odd on purpose: a two-player game can never tie, so there is always a clean winner.

Edges are addressed by orientation and grid position:

• A horizontal edge H(r, c) runs left-to-right. It is the top of box (r, c) and the bottom of box (r-1, c). Valid for r in 0..=5, c in 0..5.
• A vertical edge V(r, c) runs top-to-bottom. It is the left of box (r, c) and the right of box (r, c-1). Valid for r in 0..5, c in 0..=5.

Box (r, c) is bounded by H(r, c) (top), H(r+1, c) (bottom), V(r, c) (left), and V(r, c+1) (right).

Turns

The game is not simultaneous. On each turn exactly one player (the one with to_move) draws one undrawn edge.

• If that edge closes one or two boxes, the mover claims them and moves again.
• Otherwise the turn passes to the other player.

Seat 0 moves first. Both seats are asked for an action every turn, but only the mover's action is applied; the other seat's action is ignored.

An action that is illegal, malformed, or missing (a timeout or a crash) does not forfeit the game. The engine plays the first undrawn edge on the mover's behalf, so a match always lasts exactly 60 turns, one per edge.

Observation

Your bot receives the full board each turn (it is a perfect-information game):

{
  "you": 0,
  "to_move": 0,
  "rows": 5,
  "cols": 5,
  "h": [[false, false, false, false, false], ... 6 rows],
  "v": [[false, false, false, false, false, false], ... 5 rows],
  "owner": [[-1, -1, -1, -1, -1], ... 5 rows],
  "scores": [0, 0],
  "turn": 0,
  "nonce": 123456789
}

• h[r][c] / v[r][c] are true when that edge is already drawn.
• owner[r][c] is the seat that closed box (r, c), or -1 if it is still open.
• scores[seat] is the boxes claimed so far.
• to_move is whose turn it is. Act only when to_move == you; an action on the other player's turn is ignored.
• nonce is per-match entropy. The board always starts empty, so a bot that uses no randomness plays the same game every match; fold nonce into your randomness if you want variety.

Action

Name one undrawn edge:

{ "orient": "H", "r": 2, "c": 3 }

orient is "H" or "V". The edge must be in bounds and not already drawn.

Scoring

The match ends when all 60 edges are drawn. Finishing order is by boxes claimed, most first. With 25 boxes the result is always decisive.

Strategy notes

• Never pass up a box you can close.
• Avoid drawing the third side of a box: it hands a free box (and the move after it) to your opponent.

• The endgame is about chains. Whoever is forced to open the first long chain usually loses it. Strong play counts chain parity and sometimes declines the last two boxes of a chain (the "double-cross") to keep the opponent on the move. The built-in Greedy bot does the first two but not the third, so it is beatable by a bot that counts chains.

Determinism

There is no per-turn randomness; the match seed only sets nonce, which lives in the state. A replay re-runs bit-identically.