biomes.dart

final visited = <(int, int)>{};

Iterable<List<(int, int)>> getBiomes(List<List<int>> worldmap) sync* {
  visited.clear();

  for (int i = 0; i < worldmap.length; i++) {
    for (int j = 0; j < worldmap[i].length; j++) {
      if (visited.contains((i, j))) {
        continue;
      }

      yield traverse(worldmap, [(i, j)]);
    }
  }
}

List<(int, int)> traverse(
  List<List<int>> matrix,
  List<(int, int)> biome,
) {
  final last = biome.last;
  final (x, y) = last;

  visited.add((x, y));

  if (x < 0 || x >= matrix.length || y < 0 || y >= matrix[x].length) {
    return biome;
  }

  final current = matrix[x][y];

  // top
  if (x > 0 && matrix[x - 1][y] == current && !visited.contains((x - 1, y))) {
    biome.add((x - 1, y));
    traverse(matrix, biome);
  }

  // right
  if (y < matrix[x].length - 1 &&
      matrix[x][y + 1] == current &&
      !visited.contains((x, y + 1))) {
    biome.add((x, y + 1));
    traverse(matrix, biome);
  }

  // bottom
  if (x < matrix.length - 1 &&
      matrix[x + 1][y] == current &&
      !visited.contains((x + 1, y))) {
    biome.add((x + 1, y));
    traverse(matrix, biome);
  }

  // left
  if (y > 0 && matrix[x][y - 1] == current && !visited.contains((x, y - 1))) {
    biome.add((x, y - 1));
    traverse(matrix, biome);
  }

  return biome;
}