/// <summary>
/// If two cells in one segment contains the same two candidates only,
/// then these candidates in other cells can be removed.
/// </summary>
private void NakedPair(List <Cell> changes)
{
using (var cacheItem = _cache.Get <Candidates, int>())
{
var dic = cacheItem.Dictionary;
foreach (var seg in Segments)
{
if (seg.FreeCells < 3)
{
continue;
}
dic.Clear();
foreach (var cell in seg)
{
if (cell.HasValue)
{
continue;
}
if (dic.ContainsKey(cell.Candidates))
{
dic[cell.Candidates]++;
}
else
{
dic[cell.Candidates] = 1;
}
}
foreach (var pair in dic)
{
if (pair.Value < 2 || pair.Value >= seg.FreeCells)
{
continue;
}
if (CandidatesHelper.Count(pair.Key) != pair.Value)
{
continue;
}
foreach (var cell in seg)
{
if (cell.HasValue || cell.Candidates == pair.Key)
{
continue;
}
var old = cell.Candidates;
cell.RemoveCandidates(pair.Key);
if (cell.Candidates != old)
{
changes.Add(cell);
}
}
}
}
}
}
public void RemoveCandidates(Candidates candidates)
{
if (HasValue)
{
return;
}
Candidates &= ~candidates;
Possibilities = CandidatesHelper.Count(Candidates);
OnChanged();
}
public void SetCandidates(Candidates candidates)
{
if (HasValue)
{
throw new InvalidOperationException("Cell has already a value.");
}
if ((Candidates | candidates) != Candidates)
{
throw new InvalidOperationException("Cannot add new candidates.");
}
Candidates = candidates;
Possibilities = CandidatesHelper.Count(Candidates);
OnChanged();
}
public void Reset()
{
if (HasValue)
{
foreach (var seg in Segments.Keys)
{
seg.FreeCells++;
seg.Values &= ~CandidatesHelper.ToCandidate(Value);
}
}
_value = Cell.EmptyValue;
IsFixed = false;
Candidates = Cell.AllCandidates;
Possibilities = CandidatesHelper.Count(Candidates);
OnChanged();
}