private bool SearchSolution(Game game)
{
// Plan B if SearchIteration doesn't make progress.
// Make a copy of the game, and do a depth first search on possible permutations, until a feasible solution is found.
Stack<Game> gameStack = new Stack<Game>();
gameStack.Push(game);
bool result = SearchSolutionRecursive(gameStack);
Game copy = gameStack.Peek();
var unsolvedTiles = game.GetFlattenedTiles().Where(t => !t.IsSolved);
foreach (Tile tile in unsolvedTiles)
{
tile.Number = copy[tile.XIndex, tile.YIndex].Number;
}
return result;
}
private bool SolveIteration(Game game)
{
bool tileSolved = false;
IEnumerable<int> allNumbers = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
// The main idea here: first search all tiles and determine if any unsolved tiles are solvable (i.e. we can narrow the candidates to a single number).
// Then walk through all of the numbers and determine if there are any rows, columns, or squares for which that number can fit in only one of the nine tiles.
// Return true if at least one tile is solved this way (so we can try again), false otherwise.
foreach (Tile tile in game.GetFlattenedTiles())
{
if (tile.IsSolved)
continue;
IEnumerable<int> numbers = allNumbers.Except(tile.Row.Numbers)
.Except(tile.Column.Numbers)
.Except(tile.Square.Numbers);
if (numbers.Count() == 0)
{
throw new InvalidGameException();
}
if (numbers.Count() == 1)
{
tile.Number = numbers.First();
tileSolved = true;
}
}
foreach (int number in allNumbers)
{
tileSolved |= SolveForNumber(game.Rows, number);
tileSolved |= SolveForNumber(game.Columns, number);
tileSolved |= SolveForNumber(game.Squares, number);
}
return tileSolved;
}