/** {@inheritDoc} */
public boolean solve(Grid grid) {
Set<Set<Integer>> combinations = new HashSet<Set<Integer>>();
combinations =
Cell.generateCombinations(Cell.generateCandidateSet(1, 9), combinations, getSetSize());
for (Set<Integer> combination : combinations) {
if (solveHouses(grid.getHouses(), combination)) {
return true;
}
}
return false;
}
private boolean solveHouse(House house, Set<Integer> combination) {
Set<Cell> selectedCells = new TreeSet<Cell>();
for (Cell cell : house.getCells()) {
if (cell.isSolved()) {
// This house already contains a cell with
// one of this quad's numbers.
if (combination.contains(cell.getDigit())) {
return false;
}
continue;
}
Collection<Integer> cellCandidates = cell.getCandidates();
if (cellCandidates.size() > getSetSize()) {
// Can't possibly be a subset
continue;
}
Set<Integer> cellCandidatesCopy = new HashSet<Integer>(cellCandidates);
cellCandidatesCopy.removeAll(combination);
if (cellCandidatesCopy.size() == 0) {
selectedCells.add(cell);
}
}
if (selectedCells.size() == getSetSize()) {
Set<Cell> houseCells = new HashSet<Cell>(house.getCells());
houseCells.removeAll(selectedCells);
boolean changed = false;
for (Cell cell : houseCells) {
if (cell.removeAll(combination)) {
changed = true;
}
}
return changed;
}
return false;
}