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#include <fstream>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <string>
#include <tuple>
#include <vector>
using namespace std;
using pos_type = tuple<size_t, size_t>;
map<pos_type, int>
read_file(string_view filename)
{
fstream input{ filename };
map<pos_type, int> data;
size_t yPos = 0;
for ( string line; getline(input, line); ) {
for ( size_t xPos = 0; xPos != line.size(); ++xPos ) {
data[{ xPos, yPos }] = line.at(xPos) - '0';
}
++yPos;
}
return data;
}
constexpr vector<pos_type>
neighbors(pos_type pos)
{
const auto [x, y] = pos;
return { { x - 1, y }, { x, y - 1 }, { x + 1, y }, { x, y + 1 } };
}
vector<pos_type>
get_starts(const map<pos_type, int>& data)
{
vector<pos_type> starts;
for ( const auto& [pos, value]: data ) {
if ( value == 0 ) {
starts.push_back(pos);
}
}
return starts;
}
template<typename BFS>
size_t
solve(const map<pos_type, int>& data, BFS bfs)
{
auto starts = get_starts(data);
return accumulate(starts.begin(), starts.end(), 0U, [&](auto init, auto start) { return init + bfs(data, start); });
}
void
part1(const map<pos_type, int>& data)
{
auto bfs = [](const map<pos_type, int>& data, pos_type start_pos) -> size_t {
size_t score = 0;
set<pos_type> seen;
queue<pos_type> queue;
queue.emplace(start_pos);
seen.emplace(start_pos);
while ( !queue.empty() ) {
auto pos = queue.front();
queue.pop();
if ( data.at(pos) == 9 ) {
++score;
continue;
}
for ( const auto& neighbor: neighbors(pos) ) {
if ( !data.contains(neighbor) ||
seen.contains(neighbor) ||
data.at(neighbor) != data.at(pos) + 1 ) {
continue;
}
queue.emplace(neighbor);
seen.insert(neighbor);
}
}
return score;
};
cout << solve(data, bfs) << endl;
}
void
part2(const map<pos_type, int>& data)
{
auto bfs = [](const map<pos_type, int>& data, pos_type start_pos) -> size_t {
size_t score = 0;
queue<pos_type> queue;
queue.push(start_pos);
while ( !queue.empty() ) {
auto pos = queue.front();
queue.pop();
if ( data.at(pos) == 9 ) {
++score;
continue;
}
for ( const auto& neighbor: neighbors(pos) ) {
if ( !data.contains(neighbor) ||
data.at(neighbor) != data.at(pos) + 1 ) {
continue;
}
queue.emplace(neighbor);
}
}
return score;
};
cout << solve(data, bfs) << endl;
}
int
main()
{
auto data = read_file("data/day10.txt");
part1(data);
part2(data);
}
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