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#include <fstream>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <tuple>
#include <vector>
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.at(xPos);
}
++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 } };
}
void
part1(const map<pos_type, char>& data)
{
auto data_copy = data;
auto flood_fill = [&](pos_type start) {
set<pos_type> area;
queue<pos_type> queue;
queue.push(start);
while ( !queue.empty() ) {
auto pos = queue.front();
queue.pop();
if ( !data_copy.contains(pos) ) {
continue;
}
auto digit = data_copy.at(pos);
for ( const auto& neighbor: neighbors(pos) ) {
if ( !data_copy.contains(neighbor) ) {
continue;
}
if ( data_copy.at(neighbor) != digit ) {
continue;
}
queue.push(neighbor);
}
area.insert(pos);
data_copy.erase(pos);
}
return area;
};
auto count_edges = [](const set<pos_type>& area) -> size_t {
size_t sum = 0;
for ( const auto& pos: area ) {
for ( const auto& neighbor: neighbors(pos) ) {
if ( !area.contains(neighbor) ) {
++sum;
}
}
}
return sum;
};
size_t sum = 0;
while ( !data_copy.empty() ) {
auto area = flood_fill(data_copy.begin()->first);
auto edges = count_edges(area);
sum += area.size() * edges;
}
cout << sum << endl;
}
int
main()
{
auto data = read_file("data/day12.txt");
part1(data);
}
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