/// <summary>
/// Add a <see cref="ConstraintHeader"/> connecting all the
/// <see cref="PossibleValue"/>s at the given <paramref name="valueIndex"/> on the
/// given <paramref name="squares"/>. Skips null squares, null possible values, and any
/// possible values in a known state (i.e. dropped or selected).
/// </summary>
/// <param name="squares">The squares to add possible square values from.</param>
/// <param name="valueIndex">
/// The value index of the possible value within the squares.
/// </param>
/// <param name="matrix">The matrix for the current puzzle being solved.</param>
public static void AddConstraintHeadersForValueIndex(
ReadOnlySpan <Square?> squares, int valueIndex, ExactCoverMatrix matrix)
{
var possibleSquares = new PossibleValue[squares.Length];
int numPossibleSquares = 0;
for (int i = 0; i < squares.Length; i++)
{
Square?square = squares[i];
if (square is null)
{
continue;
}
PossibleValue?possibleSquare = square.GetPossibleValue(valueIndex);
if (possibleSquare is null ||
possibleSquare.State != PossibleSquareState.UNKNOWN)
{
continue;
}
possibleSquares[numPossibleSquares++] = possibleSquare;
}
ConstraintHeader.CreateConnectedHeader(
matrix,
new ReadOnlySpan <PossibleValue>(possibleSquares, 0, numPossibleSquares));
}
public void TryRemoveFromConstraint_OnSuccess()
{
var puzzle = new Puzzle(4);
var matrix = new ExactCoverMatrix(puzzle);
var constraintHeader = ConstraintHeader.CreateConnectedHeader(
matrix,
matrix.GetSquaresOnRow(0).ToArray().Select(s => s.AllPossibleValues[0]).ToArray());
Link firstLink = constraintHeader.FirstLink;
Link secondLink = firstLink.Down;
Link thirdLink = secondLink.Down;
Link fourthLink = thirdLink.Down;
Assert.True(firstLink.TryRemoveFromConstraint());
Assert.Same(fourthLink, firstLink.Up);
Assert.Same(secondLink, firstLink.Down);
Assert.Same(secondLink, constraintHeader.FirstLink);
Assert.Same(fourthLink, secondLink.Up);
Assert.Same(secondLink, fourthLink.Down);
Assert.Equal(3, constraintHeader.Count);
}
public void TryRemoveFromConstraint_WhenConstraintSatisfied_LeavesUnchanged()
{
var puzzle = new Puzzle(4);
var matrix = new ExactCoverMatrix(puzzle);
var constraintHeader = ConstraintHeader.CreateConnectedHeader(
matrix,
matrix.GetSquaresOnRow(0).ToArray().Select(s => s.AllPossibleValues[0]).ToArray());
Link firstLink = constraintHeader.FirstLink;
Link secondLink = firstLink.Down;
Link thirdLink = secondLink.Down;
Link fourthLink = thirdLink.Down;
int expectedConstraintCount = constraintHeader.Count;
Assert.True(firstLink.TrySatisfyConstraint());
Assert.True(secondLink.TryRemoveFromConstraint());
Assert.Equal(expectedConstraintCount, constraintHeader.Count);
Assert.Same(firstLink, secondLink.Up);
Assert.Same(secondLink, firstLink.Down);
Assert.Same(secondLink, thirdLink.Up);
Assert.Same(thirdLink, secondLink.Down);
}
