//XYwing is an algorithm that consists of two WeakLinks with common cells.
//http://csdenpe.web.fc2.com/page42.html
public bool XYwing( )
{
Prepare();
CeLKMan.PrepareCellLink(2); //Generate WeakLinks
if (BVCellLst == null)
{
BVCellLst = pBDL.FindAll(p => (p.FreeBC == 2)); //Generate BVs(BV:bivalue).
}
if (BVCellLst.Count < 3)
{
return(false);
}
bool XYwing = false;
foreach (var P0 in BVCellLst) //Choose one BV_Cell(=>PS)
{
List <UCellLink> BVLKLst = CeLKMan.IEGetRcNoBTypB(P0.rc, 0x1FF, 2).Where(R => R.BVFlag).ToList();
//Extract WeakLinks starting from P0
//foreach( var P in BVLKLst ) WriteLine(P);
if (BVLKLst.Count < 2)
{
continue;
}
var cmb = new Combination(BVLKLst.Count, 2);
int nxt = 1;
while (cmb.Successor(nxt)) //Combine two WLinks from BVLKLst
{
UCellLink LKA = BVLKLst[cmb.Index[0]], LKB = BVLKLst[cmb.Index[1]]; //(
UCell Q = LKA.UCe2, R = LKB.UCe2;
if (Q.rc == R.rc || LKA.no == LKB.no)
{
continue; //Two WLinks have different end and different digits
}
Bit81 Q81 = ConnectedCells[LKA.rc2] & ConnectedCells[LKB.rc2];
if (Q81.Count <= 0)
{
continue; //Two WLinks have cells connected indirectly
}
int noB = Q.FreeB.DifSet(1 << LKA.no) & R.FreeB.DifSet(1 << LKB.no);
if (noB == 0)
{
continue; //Two WLinks have common digit(=>no).
}
int no = noB.BitToNum();
string msg2 = "";
foreach (var A in Q81.IEGetUCeNoB(pBDL, noB))
{
if (A == P0 || A == Q || A == R)
{
continue;
}
A.CancelB = noB; XYwing = true; //cell(A)/digit(no) can be excluded
if (SolInfoB)
{
msg2 += $" {A.rc.ToRCNCLString()}(#{no+1})";
}
}
if (XYwing)
{
SolCode = 2;
P0.SetNoBColor(P0.FreeB, AttCr); P0.SetCellBgColor(SolBkCr);
Q.SetCellBgColor(SolBkCr); R.SetCellBgColor(SolBkCr);
string msg0 = $" Pivot: {_XYwingResSub(P0)}";
string msg1 = $" Pin: {_XYwingResSub(R)} ,{_XYwingResSub(Q)}";
Result = "XY Wing" + msg0;
if (SolInfoB)
{
ResultLong = $"XY Wing\r {msg0}\r {msg1}\r Eliminated:{msg2}";
}
if (__SimpleAnalizerB__)
{
return(true);
}
if (!pAnMan.SnapSaveGP())
{
return(true);
}
XYwing = false;
}
}
}
return(false);
}
//EmptyRectangle is an algorithm using cell-to-cell link and ConnectedCells.
//http://csdenpe.web.fc2.com/page41.html
public bool EmptyRectangle( )
{
Prepare();
CeLKMan.PrepareCellLink(1); //Generate StrongLink
for (int no = 0; no < 9; no++) //Focused digit
{
int noB = 1 << no;
for (int bx = 0; bx < 9; bx++) //Focused Block
{
int erB = pBDL.IEGetCellInHouse(bx + 18, noB).Aggregate(0, (Q, P) => Q | (1 << P.nx));
if (erB == 0)
{
continue;
}
for (int er = 0; er < 9; er++) //Focused Cell in the Focused Block
{
int Lr = er / 3, Lc = er % 3; //Block local Row and Column
int rxF = 7 << (Lr * 3); //7=1+2+4 (Block local Row r1c123)
int cxF = 73 << Lc; //73=1+8+64 (Block local Column r123c1)
if ((erB & rxF) == 0 || erB.DifSet(rxF) == 0)
{
continue; //Row Lr(Row Cndition Check)
}
if ((erB & cxF) == 0 || erB.DifSet(cxF) == 0)
{
continue; //Column Lc(Column Cndition Check)
}
if (erB.DifSet(rxF | cxF) > 0)
{
continue; //Row Lr and Column Lc(ER Condition Check)
}
int r1 = bx / 3 * 3 + Lr; //Convert to Absolute Row
int c1 = (bx % 3) * 3 + Lc; //Convert to Absolute Column
foreach (var P in HouseCells[9 + c1].IEGetUCeNoB(pBDL, noB).Where(Q => Q.b != bx))
{
//P:cell in house(column c1), P is outside bx
foreach (var LK in CeLKMan.IEGetRcNoBTypB(P.rc, noB, 1))//rc:link end, noB:digit, 1:StrongLink
{
UCell Elm = pBDL[r1 * 9 + LK.UCe2.c];
if (Elm.b != bx && (Elm.FreeB & noB) > 0) //There is a Digit that can be excluded
{
EmptyRectangle_SolResult(no, bx, LK, Elm); //solution found
if (__SimpleAnalizerB__)
{
return(true);
}
if (!pAnMan.SnapSaveGP(true))
{
return(true);
}
}
}
}
foreach (var P in HouseCells[0 + r1].IEGetUCeNoB(pBDL, noB).Where(Q => Q.b != bx))
{
//P:cell in house(row r1), P is outside bx
foreach (var LK in CeLKMan.IEGetRcNoBTypB(P.rc, noB, 1))//rc:link end, noB:digit, 1:StrongLink
{
UCell Elm = pBDL[LK.UCe2.r * 9 + c1];
if (Elm.b != bx && (Elm.FreeB & noB) > 0) //There is a Digit that can be excluded
{
EmptyRectangle_SolResult(no, bx, LK, Elm); //solution found
if (__SimpleAnalizerB__)
{
return(true);
}
if (!pAnMan.SnapSaveGP(true))
{
return(true);
}
}
}
}
}
}
}
return(false);
}