StepCode EliminateNakedPairsStep::runOnHouse(House &cell_list) {
bool modified = false;
std::set<Mask> found_masks;
std::set<Mask> duplicate_masks;
for (const Cell *cell : cell_list) {
if (cell->candidates.none()) {
return {true, modified};
}
if (cell->candidates.count() != 2) {
continue;
}
const Mask mask = cell->candidates.to_ulong();
if (found_masks.count(mask)) {
duplicate_masks.insert(cell->candidates.to_ulong());
}
found_masks.insert(mask);
}
for (auto &mask : duplicate_masks) {
for (Cell *cell : cell_list) {
if (cell->isFixed()) {
continue;
}
CandidateSet *candidates = &cell->candidates;
if (candidates->to_ulong() == mask) {
continue;
}
auto new_cands = CandidateSet(candidates->to_ulong() & ~mask);
if (*candidates == new_cands) {
continue;
}
if (DEBUG) {
const Mask intersection = candidates->to_ulong() & mask;
dbgs() << "Naked Pair " << printCandidateString(mask) << " removes "
<< printCandidateString(intersection) << " from " << cell->coord
<< "\n";
}
modified = true;
changed.insert(cell);
*candidates = new_cands;
}
}
return {false, modified};
}
StepCode EliminateNakedTriplesStep::runOnHouse(House &house) {
bool modified = false;
if (house.size() <= 3) {
return {false, modified};
}
std::vector<std::pair<Mask, std::vector<const Cell *>>> found_masks;
for (const Cell *cell : house) {
std::size_t num_candidates = cell->candidates.count();
if (num_candidates == 0) {
return {true, modified};
}
if (num_candidates != 2 && num_candidates != 3) {
continue;
}
const Mask mask = cell->candidates.to_ulong();
bool found_match = false;
for (unsigned i = 0; i < found_masks.size(); ++i) {
const Mask m = found_masks[i].first;
// ORing the two masks together will switch on all candidates found in
// both masks. If it's less than three, then we're still a triple
// candidate.
// TODO: If the current mask is size 2 and the OR of the two is 3, then
// we should create two masks: one for the two and one for the OR.
// Otherwise you could get 1/2 match with 1/2/3 and 1/2/4.
// For now, only accept found masks of size 3. Easy naked triples.
if (bitCount(m) == 3 && bitCount(mask | m) == 3) {
found_match = true;
found_masks[i].second.push_back(cell);
}
}
if (!found_match) {
std::pair<Mask, std::vector<const Cell *>> pair;
pair.first = mask;
pair.second.push_back(cell);
found_masks.push_back(pair);
}
}
for (auto &pair : found_masks) {
if (pair.second.size() != 3) {
continue;
}
auto &matches = pair.second;
const Mask mask = pair.first;
for (Cell *cell : house) {
if (cell->isFixed()) {
continue;
}
if (std::find(matches.begin(), matches.end(), cell) != matches.end()) {
continue;
}
CandidateSet *candidates = &cell->candidates;
if (candidates->to_ulong() == mask) {
continue;
}
auto new_cands = CandidateSet(candidates->to_ulong() & ~mask);
if (*candidates == new_cands) {
continue;
}
if (DEBUG) {
const Mask intersection = candidates->to_ulong() & mask;
dbgs() << "Naked Triple " << printCandidateString(mask) << " removes "
<< printCandidateString(intersection) << " from " << cell->coord
<< "\n";
}
modified = true;
changed.insert(cell);
*candidates = new_cands;
}
}
return {false, modified};
}
