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#include <fstream>
#include <iostream>
#include <map>
#include <set>
#include <string>
#include <tuple>
using namespace std;
using pos_type = tuple<size_t, size_t>;
map<pos_type, char>
read_file(string_view filename)
{
fstream input{ filename };
map<pos_type, char> data;
size_t yPos = 0;
for ( string line; getline(input, line); ) {
for ( size_t xPos = 0; xPos != line.size(); ++xPos ) {
data[{ xPos, yPos }] = line[xPos];
}
++yPos;
}
return data;
}
set<pos_type>
distinct_positions(const map<pos_type, char>& data)
{
static const array<pos_type, 4> deltas = {
make_tuple(0, -1),
make_tuple(1, 0),
make_tuple(0, 1),
make_tuple(-1, 0)
};
size_t direction = 0;
auto position = get<0>(*ranges::find_if(data, [](auto position) {
return get<1>(position) == '^';
}));
set<pos_type> positions;
while ( true ) {
positions.emplace(position);
auto next_position = make_tuple(get<0>(position) + get<0>(deltas.at(direction)),
get<1>(position) + get<1>(deltas.at(direction)));
if ( !data.contains(next_position) ) {
break;
}
if ( data.at(next_position) == '#' ) {
direction = (direction + 1) % deltas.size();
}
else {
position = next_position;
}
}
return positions;
}
void
part1(const map<pos_type, char>& data)
{
auto positions = distinct_positions(data);
cout << positions.size() << endl;
}
bool
would_loop(const map<pos_type, char>& data)
{
static const array<pos_type, 4> deltas = {
make_tuple(0, -1),
make_tuple(1, 0),
make_tuple(0, 1),
make_tuple(-1, 0)
};
size_t direction = 0;
auto position = get<0>(*ranges::find_if(data, [](auto position) {
return get<1>(position) == '^';
}));
set<tuple<pos_type, size_t>> positions;
while ( true ) {
positions.emplace(position, direction);
auto next_position = make_tuple(get<0>(position) + get<0>(deltas.at(direction)),
get<1>(position) + get<1>(deltas.at(direction)));
if ( !data.contains(next_position) ) {
return false;
}
if ( data.at(next_position) == '#' ) {
direction = (direction + 1) % deltas.size();
}
else {
position = next_position;
}
if ( positions.contains({ position, direction }) ) {
return true;
}
}
}
void
part2(map<pos_type, char> data)
{
const auto positions = distinct_positions(data);
long sum = 0;
for ( const auto& position: positions ) {
if ( data.at(position) == '.' ) {
data.at(position) = '#';
if ( would_loop(data) ) {
++sum;
}
data.at(position) = '.';
}
}
cout << sum << endl;
}
int
main()
{
auto data = read_file("data/day06.txt");
part1(data);
part2(data);
}
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