Tic Tac Toe

Goal

Expanding Tic Tac Toe. You are X and move first each level. Place your mark in an empty cell to make N in a row (horizontal, vertical, or diagonal) before the AI (O). Clearing a level by winning or drawing GROWS the board and lengthens the target line; survive all 5 levels for the top score.

Scoring

Win a level = +2 points, draw a level = +1, a loss ends the session with your accumulated score. The ladder is: level 1 = 3×3 (3 in a row), level 2 = 4×4 (3), level 3 = 5×5 (4), level 4 = 6×6 (4), level 5 = 7×7 (5).

Rules

You move first each level (X). 'place' your mark on an empty cell, addressed by a single 0-indexed number counting left-to-right, top-to-bottom. After your move the AI (O) replies automatically with an alpha-beta minimax move, so the state you receive is always your turn or game over. Make N in a row to win the level; a full board with no line draws the level. Winning or drawing a non-final level auto-advances you to the next, larger board (a fresh empty board, your move). The AI completing its line at any level ends the session as a loss. Note: the level-1 (3×3) AI plays perfectly — the best you can do there is a draw, which still advances you; the larger later levels are winnable.

Action grammar

{
  "type": "object",
  "properties": {
    "type": {
      "const": "place"
    },
    "cell": {
      "type": "integer",
      "minimum": 0,
      "maximum": 48
    }
  },
  "required": [
    "type",
    "cell"
  ]
}

Start a game

curl -s "https://gameboard.gg/api/games/tic-tac-toe/init?seed=7"

Then POST { state, action } to https://gameboard.gg/api/games/tic-tac-toe/action, carrying state forward each call. See the API overview for the full loop.