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pond_solver.cc
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pond_solver.cc
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#include "pond_solver.h"
using std::cin;
using std::cout;
using std::endl;
using std::pair;
using std::priority_queue;
using std::string;
using std::unordered_map;
using std::unordered_set;
using std::vector;
using BoardState = long long int;
namespace {
constexpr const int kBoardDimension = 6;
}
void Board::AddPiece(const Piece piece) { pieces_.push_back(piece); }
bool Board::Win() { return pieces_[0].moving_axis_pos == kBoardDimension - 2; }
MoveStatus Board::MovePiece(int i, int new_pos, BoardState previous_state, int current_steps) {
if (pieces_[i].size + new_pos > kBoardDimension) {
return MoveStatus::OUT_OF_BOUNDARY;
}
int old_pos = pieces_[i].moving_axis_pos;
pieces_[i].moving_axis_pos = new_pos;
if (!IsValid(i)) {
pieces_[i].moving_axis_pos = old_pos;
return MoveStatus::OVERLAPPED;
}
if (simulation_mode_) {
return MoveStatus::OK;
}
BoardState state = GetBoardState();
if (IsVisited(state)) {
pieces_[i].moving_axis_pos = old_pos;
return MoveStatus::VISITED;
}
prev_state_of_state_[state] =
pair<BoardState, pair<int, int>>(previous_state, pair<int, int>(i, new_pos));
return MoveStatus::OK;
}
bool Board::IsValid(int moved_index) {
for (int i = 0; i < pieces_.size(); i++) {
if (i == moved_index) {
continue;
}
unordered_set<int> i_occurrencies;
// Fill i's occurrencies.
if (pieces_[i].direction == Direction::VERTICAL) {
for (int k = pieces_[i].moving_axis_pos; k < pieces_[i].moving_axis_pos + pieces_[i].size;
k++) {
int state = (pieces_[i].fix_axis_pos << 16) + k;
i_occurrencies.insert(state);
}
} else {
for (int k = pieces_[i].moving_axis_pos; k < pieces_[i].moving_axis_pos + pieces_[i].size;
k++) {
int state = (k << 16) + pieces_[i].fix_axis_pos;
i_occurrencies.insert(state);
}
}
int j = moved_index;
// Check each of j's occupancy.
if (pieces_[j].direction == Direction::VERTICAL) {
for (int k = pieces_[j].moving_axis_pos; k < pieces_[j].moving_axis_pos + pieces_[j].size;
k++) {
int state = (pieces_[j].fix_axis_pos << 16) + k;
if (i_occurrencies.count(state)) {
return false;
}
}
} else {
for (int k = pieces_[j].moving_axis_pos; k < pieces_[j].moving_axis_pos + pieces_[j].size;
k++) {
int state = (k << 16) + pieces_[j].fix_axis_pos;
if (i_occurrencies.count(state)) {
return false;
}
}
}
}
return true;
}
BoardState Board::GetBoardState() {
BoardState state = 0;
for (int i = 0; i < pieces_.size(); i++) {
long long int i_moving_axis_pos_64 = pieces_[i].moving_axis_pos;
state += (i_moving_axis_pos_64 << (i * 3));
}
return state;
}
void Board::ResumeState(BoardState state) {
for (int i = 0; i < pieces_.size(); i++) {
pieces_[i].moving_axis_pos = (state >> (i * 3)) % 8;
}
}
bool Board::IsVisited(BoardState state) { return prev_state_of_state_.count(state); }
void Board::SolveAll() {
// Save initial states.
BoardState initial_state = GetBoardState();
prev_state_of_state_[initial_state] =
pair<BoardState, pair<int, int>>(-1, pair<int, int>(-1, -1));
queue_.push(std::make_pair(0, initial_state));
int result = Solve();
if (result != -1) {
cout << "Win! " << result << endl;
BoardState state = win_state_;
while (prev_state_of_state_[state].first != -1) {
cout << prev_state_of_state_[state].second.first << ' '
<< prev_state_of_state_[state].second.second << endl;
state = prev_state_of_state_[state].first;
}
cout << "Best solution has " << result << " steps." << endl;
} else {
cout << "Could not find a solution." << endl;
}
}
int Board::Solve() {
while (!queue_.empty()) {
int current_steps;
BoardState current_state;
std::tie(current_steps, current_state) = queue_.top();
queue_.pop();
ResumeState(current_state);
if (Win()) {
win_state_ = current_state;
return current_steps;
}
for (int i = 0; i < pieces_.size(); i++) {
int old_pos = pieces_[i].moving_axis_pos;
// up/left side
for (int j = old_pos - 1; j >= 0; j--) {
MoveStatus status = MovePiece(i, j, current_state, current_steps + 1);
if (status == MoveStatus::OUT_OF_BOUNDARY || status == MoveStatus::OVERLAPPED) {
break;
}
if (status == MoveStatus::VISITED) {
continue;
}
queue_.push(std::make_pair(current_steps + 1, GetBoardState()));
pieces_[i].moving_axis_pos = old_pos;
}
// down/right side
for (int j = old_pos + 1; j < kBoardDimension; j++) {
MoveStatus status = MovePiece(i, j, current_state, current_steps + 1);
if (status == MoveStatus::OUT_OF_BOUNDARY || status == MoveStatus::OVERLAPPED) {
break;
}
if (status == MoveStatus::VISITED) {
continue;
}
queue_.push(std::make_pair(current_steps + 1, GetBoardState()));
pieces_[i].moving_axis_pos = old_pos;
}
}
}
return -1;
}
void Board::PrintBoard() {
//
}