/// <summary>Reduces naked triples.</summary>
private ReduceResult ReduceNakedTriples(ReduceResult result, SudokuState state)
{
if (SkipMethod(SudokuSolverMethods.NakedTriples, result)) { return result; }
foreach (var singleValue in Puzzle.SingleValues)
{
foreach (var region in Puzzle.Regions)
{
var index0 = -1;
var index1 = -1;
var index2 = -1;
var match = singleValue;
foreach (var index in region)
{
var value = state[index];
if (!state.IsKnown(index) && (value & match) != SudokuPuzzle.Invalid)
{
match |= value;
/**/ if (index0 == -1) { index0 = index; }
else if (index1 == -1) { index1 = index; }
else if (index2 == -1) { index2 = index; }
else { index2 = -1; break; }
}
}
// We found 3 cells.
if (index2 != -1 && SudokuCell.Count(match) == 3)
{
foreach (var index in region)
{
if (index != index0 && index != index1 && index != index2)
{
result |= state.AndMask(index, ~match);
}
}
}
}
}
return result;
}
/// <summary>Reduces hidden singles.</summary>
/// <remarks>
/// Very frequently, there is only one candidate for a given row, column or
/// sub square, but it is hidden among other candidates.
/// </remarks>
private ReduceResult ReduceHiddenSingles(ReduceResult result, SudokuState state)
{
if (SkipMethod(SudokuSolverMethods.HiddenSingles, result)) { return result; }
foreach (var region in Puzzle.Regions)
{
foreach (var singleValue in Puzzle.SingleValues)
{
var cnt = 0;
var found = -1;
foreach (var index in region)
{
var val = state[index];
if ((val & singleValue) != SudokuPuzzle.Invalid)
{
unchecked { cnt++; }
if (state.IsKnown(index))
{
found = -1;
break;
}
else if (cnt == 1)
{
found = index;
}
}
}
if (cnt == 1 && found != -1)
{
result |= state.AndMask(found, singleValue);
}
else if (cnt == 0)
{
return ReduceResult.Inconsistend;
}
}
}
return result;
}
/// <summary>Reduces options that should be in the intersection.</summary>
private ReduceResult ReduceLockedCandidates(ReduceResult result, SudokuState state)
{
if (SkipMethod(SudokuSolverMethods.LockedCandidates, result)) { return result; }
foreach (var region in Puzzle.Regions)
{
foreach (var other in region.Intersected)
{
ulong combined = 0;
foreach (var index in region)
{
if (!other.Contains(index))
{
combined |= state[index];
}
}
// There are options that should be in the intersection.
if (combined != Puzzle.Unknown)
{
foreach (var index in other)
{
if (!region.Contains(index))
{
var val = state[index];
var nw = val & combined;
result |= state.AndMask(index, nw);
}
}
}
}
}
return result;
}