/**
* Searches for W-Wings: look for all combinations of bivalue cells with the same candidates. If
* one is found and it could theoretically eliminate something, a connecting strong link is
* searched for.
*
* @param onlyOne
* @return
*/
private SolutionStep getWWing(boolean onlyOne) {
for (int i = 0; i < sudoku.getCells().length; i++) {
if (sudoku.getValue(i) != 0 || sudoku.getAnzCandidates(i) != 2) {
continue;
}
// bivalue cell found
short cell1 = sudoku.getCell(i);
int cand1 = sudoku.getAllCandidates(i)[0];
int cand2 = sudoku.getAllCandidates(i)[1];
// prepare for elimination checks
preCalcSet1.setAnd(Sudoku2.buddies[i], finder.getCandidates()[cand1]);
preCalcSet2.setAnd(Sudoku2.buddies[i], finder.getCandidates()[cand2]);
// check all other cells
for (int j = i + 1; j < sudoku.getCells().length; j++) {
if (sudoku.getCell(j) != cell1) {
// doesnt fit!
continue;
}
// ok, we have a pair; can anything be eliminated?
elimSet.setAnd(preCalcSet1, Sudoku2.buddies[j]);
if (!elimSet.isEmpty()) {
// check for W-Wing for candidate cand1
SolutionStep step = checkLink(cand1, cand2, i, j, elimSet, onlyOne);
if (onlyOne && step != null) {
return step;
}
}
elimSet.setAnd(preCalcSet2, Sudoku2.buddies[j]);
if (!elimSet.isEmpty()) {
// check for W-Wing for candidate cand2
SolutionStep step = checkLink(cand2, cand1, i, j, elimSet, onlyOne);
if (onlyOne && step != null) {
return step;
}
}
}
}
return null;
}
/**
* Try all combinations of three bivalue cells (for xyz: one trivalue and two bivalue cells). The
* following restrictions are in place:
*
* <ul>
* <li>The three cells must have exactly three candidates together
* <li>The first cell (pivot) must see both other cells (pincers)
* <li>The pincers must have exactly one candidate that is the same (candidate z)
* <li>z can be excluded from all cells that see both pincers (for xyz they must see the pivot
* as well)
* </ul>
*
* @param xyz
* @param onlyOne
* @return
*/
private SolutionStep getWing(boolean xyz, boolean onlyOne) {
// first get all bivalue/trivalue cells
int biValueCount = 0;
int triValueCount = 0;
for (int i = 0; i < Sudoku2.LENGTH; i++) {
if (sudoku.getAnzCandidates(i) == 2) {
biCells[biValueCount++] = i;
}
if (xyz && sudoku.getAnzCandidates(i) == 3) {
triCells[triValueCount++] = i;
}
}
// now iterate them; use local variables to cover xy and xyz
int endIndex = xyz ? triValueCount : biValueCount;
int[] biTri = xyz ? triCells : biCells;
// we check all combinations of bivalue cells (one tri + 2 bi for xyz)
for (int i = 0; i < endIndex; i++) {
for (int j = xyz ? 0 : i + 1; j < biValueCount; j++) {
// any given combination of two cells must give exactly three
// candidates; if that is not the case, skip it right away
if (Sudoku2.ANZ_VALUES[sudoku.getCell(biTri[i]) | sudoku.getCell(biCells[j])] != 3) {
// cant become a wing
continue;
}
for (int k = j + 1; k < biValueCount; k++) {
int index1 = biTri[i];
int index2 = biCells[j];
int index3 = biCells[k];
int cell1 = sudoku.getCell(index1);
int cell2 = sudoku.getCell(index2);
int cell3 = sudoku.getCell(index3);
// all three cells combined must have exactly three candidates
if (Sudoku2.ANZ_VALUES[cell1 | cell2 | cell3] != 3) {
// incorrect number of candidates
continue;
}
// none of the cells may be equal
if (cell1 == cell2 || cell2 == cell3 || cell3 == cell1) {
// cant be a wing
continue;
}
// three possibilities for XY-Wing: each cell could be the pincer
// XYZ-Wing exits the loop after the first iteration
int maxTries = xyz ? 1 : 3;
for (int tries = 0; tries < maxTries; tries++) {
// swap cells accordingly
if (tries == 1) {
index1 = biCells[j];
index2 = biTri[i];
cell1 = sudoku.getCell(index1);
cell2 = sudoku.getCell(index2);
} else if (tries == 2) {
index1 = biCells[k];
index2 = biCells[j];
index3 = biTri[i];
cell1 = sudoku.getCell(index1);
cell2 = sudoku.getCell(index2);
cell3 = sudoku.getCell(index3);
}
// the pivot must see the pincers
if (!Sudoku2.buddies[index1].contains(index2)
|| !Sudoku2.buddies[index1].contains(index3)) {
// doesnt see them -> try another
continue;
}
// the pincers must have exactly one candidate that is the same in both cells
short cell = (short) (cell2 & cell3);
if (Sudoku2.ANZ_VALUES[cell] != 1) {
// no wing, sorry
continue;
}
int candZ = Sudoku2.CAND_FROM_MASK[cell];
// are there candidates that can see the pincers?
elimSet.setAnd(Sudoku2.buddies[index2], Sudoku2.buddies[index3]);
elimSet.and(finder.getCandidates()[candZ]);
if (xyz) {
// the pivot as well
elimSet.and(Sudoku2.buddies[index1]);
}
if (elimSet.isEmpty()) {
// no candidates to delete
continue;
}
// ok, wing found!
globalStep.reset();
if (xyz) {
globalStep.setType(SolutionType.XYZ_WING);
} else {
globalStep.setType(SolutionType.XY_WING);
}
int[] cands = sudoku.getAllCandidates(index1);
globalStep.addValue(cands[0]);
globalStep.addValue(cands[1]);
if (xyz) {
globalStep.addValue(cands[2]);
} else {
globalStep.addValue(candZ);
}
globalStep.addIndex(index1);
globalStep.addIndex(index2);
globalStep.addIndex(index3);
if (xyz) {
globalStep.addFin(index1, candZ);
}
globalStep.addFin(index2, candZ);
globalStep.addFin(index3, candZ);
for (int l = 0; l < elimSet.size(); l++) {
globalStep.addCandidateToDelete(elimSet.get(l), candZ);
}
SolutionStep step = (SolutionStep) globalStep.clone();
if (onlyOne) {
return step;
} else {
steps.add(step);
}
}
}
}
}
return null;
}