/// <summary>
/// Generate a puzzle with the specified information.
/// </summary>
/// <param name="max">The maximum hints of the puzzle.</param>
/// <param name="symmetricalType">
/// The symmetry type flags. The <see cref="SymmetryType"/> is
/// a flag type, you can use bit operators to accumulate multiple
/// symmetrical types such as <c><see cref="AntiDiagonal"/> | <see cref="Diagonal"/></c>,
/// which means that the solver will generate anti-diagonal type or
/// diagonal type puzzles.
/// </param>
/// <returns>The grid.</returns>
/// <seealso cref="SymmetryType"/>
public IReadOnlyGrid Generate(int max, SymmetryType symmetricalType)
{
var puzzle = new StringBuilder(Grid.EmptyString);
var solution = new StringBuilder(Grid.EmptyString);
GenerateAnswerGrid(puzzle, solution);
// Now we remove some digits from the grid.
var allTypes = from st in EnumEx.GetValues <SymmetryType>()
where st != None && symmetricalType.HasFlag(st)
select st;
int count = allTypes.Count();
if (count == 0)
{
allTypes = new[] { None };
}
var tempSb = new StringBuilder(solution.ToString());
string result;
do
{
var selectedType = allTypes.ElementAt(Rng.Next(count));
for (int i = 0; i < 81; i++)
{
solution[i] = tempSb[i];
}
var totalMap = GridMap.Empty;
do
{
int cell;
do
{
cell = Rng.Next(0, 81);
} while (totalMap[cell]);
int r = cell / 9, c = cell % 9;
// Get new value of 'last'.
var tempMap = GridMap.Empty;
foreach (int tCell in selectedType switch
{
Central => new[] { r * 9 + c, (8 - r) * 9 + 8 - c },
Diagonal => new[] { r * 9 + c, c * 9 + r },
AntiDiagonal => new[] { r * 9 + c, (8 - c) * 9 + 8 - r },
XAxis => new[] { r * 9 + c, (8 - r) * 9 + c },
YAxis => new[] { r * 9 + c, r * 9 + 8 - c },
DiagonalBoth => new[]
{
r * 9 + c, c * 9 + r, (8 - c) * 9 + 8 - r, (8 - r) * 9 + 8 - c
},
AxisBoth => new[]
{
r * 9 + c, (8 - r) * 9 + c, r * 9 + 8 - c, (8 - r) * 9 + 8 - c
},
All => new[]
{
r * 9 + c, r * 9 + (8 - c), (8 - r) * 9 + c, (8 - r) * 9 + (8 - c),
c * 9 + r, c * 9 + (8 - r), (8 - c) * 9 + r, (8 - c) * 9 + (8 - r)
},
None => new[] { r * 9 + c },
_ => throw Throwings.ImpossibleCaseWithMessage("You should not add an option that does not contain in the table of symmetrical types.")
})
{
solution[tCell] = '0';
totalMap.Add(tCell);
tempMap.Add(tCell);
}
} while (81 - totalMap.Count > max);
} while (!FastSolver.CheckValidity(result = solution.ToString(), out _));
