Causeway

Goal

You are amber on a 9x9 rhombus of 81 hexagonal basalt columns, and you move first. Each turn you raise exactly one empty column. You win the instant your amber columns form an unbroken chain of touching hexagons from your far shore (row 1, the top) to your near shore (row 9, the bottom). G-Bot raises slate teal columns and is crossing the same ground the other way, from its west shore (column A) to its east shore (column I). This is a hex-grid connection game on one shared piece of ground: nothing is ever captured or removed, so every column you raise is both a step forward for you and a wall in front of G-Bot.

Scoring

Higher is better, and the ceiling is 2000. A crossing scores 900, plus 35 for every column below 30 that you used, plus a flat difficulty bonus (Easy 0, Wise 200, Deep 365). So a nine-column crossing on Deep is the maximum 2000, and fewer columns always scores more. A round without a crossing still scores 120, plus round(600 * (bestSpan - 1) / 8) for the number of rows your largest connected amber group spanned, plus a smaller difficulty bonus (Easy 0, Wise 40, Deep 70). The worst crossing outscores the best non-crossing by at least 185, so completing your causeway always comes first.

Rules

The board is a 9x9 axial rhombus of 81 hexagonal columns. A column is addressed by axial coordinates q (0..8, west to east, labelled A..I) and r (0..8, far shore to near shore, labelled 1..9), so E5 is the centre column at q 4, r 4. Every column has up to six neighbours, at exactly the axial offsets (+1,0), (-1,0), (0,+1), (0,-1), (+1,-1) and (-1,+1). Coordinates outside 0..8 do not exist and there is no wrapping, so the four corners have fewer neighbours than the rest: (0,0) and (8,8) have two, (8,0) and (0,8) have three, other edge columns have four, and interior columns have six. Corners belong to BOTH of their shores: (0,0) is far shore and west shore, (8,0) is far shore and east shore, (0,8) is near shore and west shore, (8,8) is near shore and east shore. You always move first and you are always amber. A turn is exactly one 'claim' of one empty column; there is no pass and no resign. Nothing is ever captured, flipped, moved or removed, so a column you raise stays yours for the rest of the round. G-Bot replies automatically inside your action, so the state you receive back is always your turn again or the finished round, and you never place a teal column yourself. The win check runs after every single placement, yours and G-Bot's, and the round ends the instant one side holds an unbroken chain joining both of its own shores. Claiming an occupied or out-of-range column is refused and costs you nothing: no column is raised, no turn is spent and G-Bot does not reply. Every round has a winner. Two completed crossings would have to pass through each other, and one column cannot be two colours, so at most one crossing can ever exist, and a completely full rhombus always contains exactly one. There is no tie and no stalemate, and the round always ends within 81 placements.

Action grammar

{
  "type": "object",
  "properties": {
    "type": {
      "const": "claim"
    },
    "q": {
      "type": "integer",
      "minimum": 0,
      "maximum": 8
    },
    "r": {
      "type": "integer",
      "minimum": 0,
      "maximum": 8
    }
  },
  "required": [
    "type",
    "q",
    "r"
  ]
}

Start a game

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

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