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#include <fstream>
#include <iostream>
#include <map>
#include <optional>
#include <set>
#include <string>
#include <tuple>
using namespace std;
using pos_type = tuple<size_t, size_t>;
using room_type = set<pos_type>;
using boxes_type = set<pos_type>;
using puzzle_type = tuple<room_type, boxes_type, string, pos_type>;
puzzle_type
read_file(string_view filename)
{
fstream input{ filename };
room_type room;
boxes_type boxes;
string movements;
pos_type start;
size_t yPos = 0;
for ( string line; getline(input, line); ) {
if ( line.empty() ) {
continue;
}
if ( line[0] == '#' ) {
for ( size_t xPos = 0; xPos != line.size(); ++xPos ) {
auto chr = line.at(xPos);
if ( chr == '#' ) {
room.emplace(xPos, yPos);
}
else if ( chr == 'O' ) {
boxes.emplace(xPos, yPos);
}
else if ( chr == '@' ) {
start = { xPos, yPos };
}
}
++yPos;
}
else {
movements += line;
}
}
return { room, boxes, movements, start };
}
void
print(const room_type& room, const boxes_type& boxes, const pos_type& pos)
{
for ( size_t yPos = 0; yPos != 10; ++yPos ) {
for ( size_t xPos = 0; xPos != 10; ++xPos ) {
if ( pos == pos_type{ xPos, yPos } ) {
cout << '@';
}
else if ( room.contains({ xPos, yPos }) ) {
cout << '#';
}
else if ( boxes.contains({ xPos, yPos }) ) {
cout << 'O';
}
else {
cout << ' ';
}
}
cout << '\n';
}
cout << endl;
}
optional<boxes_type>
can_move(const room_type& room, const boxes_type& boxes, pos_type start, pos_type direction) // NOLINT
{
const auto [x, y] = start;
const auto [dx, dy] = direction;
boxes_type candidates;
size_t steps = 1;
while ( boxes.contains({ x + dx * steps, y + dy * steps }) ) {
candidates.insert({ x + dx * steps, y + dy * steps });
++steps;
}
if ( room.contains({ x + dx * steps, y + dy * steps }) ) {
return nullopt;
}
return candidates;
}
void
part1(const puzzle_type& puzzle)
{
map<char, pos_type> deltas = {
{ '<', { -1, 0 } }, // Left
{ '^', { 0, -1 } }, // Up
{ '>', { 1, 0 } }, // Right
{ 'v', { 0, 1 } } // Down
};
auto [room, boxes, movements, start] = puzzle;
for ( auto chr: movements ) {
const auto delta = deltas[chr];
if ( auto bitw = can_move(room, boxes, start, delta) ) {
const auto [dx, dy] = delta;
get<0>(start) += dx;
get<1>(start) += dy;
boxes_type new_boxes;
for ( const auto& box: boxes ) {
if ( bitw->contains(box) ) {
const auto [x, y] = box;
new_boxes.emplace(x + dx, y + dy);
bitw->erase(box);
}
else {
new_boxes.insert(box);
}
}
boxes = new_boxes;
}
}
size_t sum = 0;
for (const auto& [x, y]: boxes) {
sum += x + 100 * y;
}
cout << sum << endl;
}
int
main()
{
const auto data = read_file("data/day15.txt");
part1(data);
}
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