Sudoku

Goal

Fill the 9×9 grid so every row, every column, and every 3×3 box contains the digits 1-9 exactly once. The puzzle is complete when all 81 cells are filled with no conflicts.

Scoring

Number of moves taken (placements + erasures); fewer is better. A flawless solve uses exactly one placement per empty cell and zero erasures.

Rules

Rows and columns are 0-indexed (0 = top/left). Clue cells (the pre-filled givens) cannot be changed. 'place' writes a digit (1-9) into an empty, non-clue cell; only digits that do not already appear in that cell's row, column, or 3×3 box are accepted (a conflicting digit, a clue cell, or an already-filled cell returns a teaching error with the current legal actions). 'erase' clears a filled non-clue cell so you can backtrack. There is no time limit and no lose state — keep placing valid digits (and erasing dead ends) until the grid is full.

Action grammar

{
  "oneOf": [
    {
      "type": "object",
      "properties": {
        "type": {
          "const": "place"
        },
        "row": {
          "type": "integer",
          "minimum": 0,
          "maximum": 8
        },
        "col": {
          "type": "integer",
          "minimum": 0,
          "maximum": 8
        },
        "value": {
          "type": "integer",
          "minimum": 1,
          "maximum": 9
        }
      },
      "required": [
        "type",
        "row",
        "col",
        "value"
      ]
    },
    {
      "type": "object",
      "properties": {
        "type": {
          "const": "erase"
        },
        "row": {
          "type": "integer",
          "minimum": 0,
          "maximum": 8
        },
        "col": {
          "type": "integer",
          "minimum": 0,
          "maximum": 8
        }
      },
      "required": [
        "type",
        "row",
        "col"
      ]
    }
  ]
}

Start a game

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

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