/// <summary>Override; see base.</summary>
public override ConstraintResult Process(SolverState state)
{
state.MarkImpossible(AffectedCells[0], value => value < 0 || value >= AffectedCells.Length || state.IsImpossible(AffectedCells[value], Value));
if (state.LastPlacedCell == AffectedCells[0])
{
// The focus cell has been set, therefore place the value in the correct position
state.MustBe(AffectedCells[state.LastPlacedValue], Value);
}
return(null);
}
/// <summary>Override; see base.</summary>
public override ConstraintResult Process(SolverState state)
{
state.MustBe(Cell, Value);
return(ConstraintResult.Remove);
}
/// <summary>Override; see base.</summary>
public override ConstraintResult Process(SolverState state)
{
if (state.LastPlacedCell != null)
{
foreach (var cell in AffectedCells)
{
if (cell != state.LastPlacedCell.Value)
{
state.MarkImpossible(cell, state.LastPlacedValue);
}
}
}
else
{
// In case this constraint was returned from another constraint when some of the grid is already filled in, make sure to enforce uniqueness correctly.
foreach (var cell1 in AffectedCells)
{
if (state[cell1] != null)
{
foreach (var cell2 in AffectedCells)
{
if (cell2 != cell1)
{
state.MarkImpossible(cell2, state[cell1].Value);
}
}
}
}
}
// Special case: if the number of values equals the number of cells, we can detect further optimizations
if (state.MaxValue - state.MinValue + 1 == AffectedCells.Length)
{
if (_optimizationList == null || _optimizationList.Length != state.MaxValue - state.MinValue + 1)
{
_optimizationList = new List <int> [state.MaxValue - state.MinValue + 1];
}
var cells = _optimizationList;
for (var i = 0; i < cells.Length; i++)
{
if (cells[i] != null)
{
cells[i].Clear();
}
}
foreach (var cell in AffectedCells)
{
for (var v = state.MinValue; v <= state.MaxValue; v++)
{
if (!state.IsImpossible(cell, v))
{
if (cells[v - state.MinValue] == null)
{
cells[v - state.MinValue] = new List <int>();
}
cells[v - state.MinValue].Add(cell);
}
}
}
for (var v1 = 0; v1 <= state.MaxValue - state.MinValue; v1++)
{
// Detect if a value can only be in one place
if (cells[v1]?.Count == 1)
{
state.MustBe(cells[v1][0], v1 + state.MinValue);
}
for (var v2 = v1 + 1; v2 <= state.MaxValue - state.MinValue; v2++)
{
// Detect if two values can only be in two places (“pair”)
if (cells[v1]?.Count == 2 && cells[v2]?.Count == 2 && cells[v1].All(cells[v2].Contains))
{
foreach (var c in cells[v1])
{
state.MarkImpossible(c, v => v != v1 + state.MinValue && v != v2 + state.MinValue);
}
}
for (var v3 = v2 + 1; v3 <= state.MaxValue - state.MinValue; v3++)
{
// Detect if three values can only be in three places (“triplet”)
if (cells[v1]?.Count <= 3 && cells[v2]?.Count <= 3 && cells[v3]?.Count <= 3)
{
var hashSet = new HashSet <int>(cells[v1]);
hashSet.AddRange(cells[v2]);
hashSet.AddRange(cells[v3]);
if (hashSet.Count <= 3)
{
foreach (var c in hashSet)
{
state.MarkImpossible(c, v => v != v1 + state.MinValue && v != v2 + state.MinValue && v != v3 + state.MinValue);
}
}
}
}
}
}
}
return(null);
}
