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#include <cstddef>
#include <fstream>
#include <iostream>
#include <map>
#include <queue>
#include <regex>
#include <set>
#include <tuple>
#include <vector>
using namespace std;
using pos_type = tuple<long, long>;
using velo_type = tuple<long, long>;
vector<tuple<pos_type, velo_type>>
read_file(string_view filename)
{
static const regex pattern{ R"(^p=(-?\d+),(-?\d+) v=(-?\d+),(-?\d+)$)" };
fstream input{ filename };
vector<tuple<pos_type, velo_type>> data;
for ( string line; getline(input, line); ) {
smatch matches;
if ( regex_search(line, matches, pattern) ) {
data.push_back({ { stoi(matches[1]), stoi(matches[2]) },
{ stoi(matches[3]), stoi(matches[4]) } });
}
}
return data;
}
/*
void
print(const vector<tuple<pos_type, velo_type>>& robots, long width, long height)
{
map<pos_type, long> map;
for ( const auto& [pos, velo]: robots ) {
map[pos]++;
}
for ( long y = 0; y != height; ++y ) {
for ( long x = 0; x != width; ++x ) {
auto pos = map.find({ x, y });
if ( pos != map.end() ) {
cout << pos->second;
}
else {
cout << '.';
}
}
cout << '\n';
}
cout << endl;
}
*/
/*
void
print_pic(const vector<tuple<pos_type, velo_type>>& robots, long width, long height)
{
map<pos_type, long> map;
for ( const auto& [pos, velo]: robots ) {
map[pos]++;
}
for ( long y = 0; y != height; ++y ) {
for ( long x = 0; x != width; ++x ) {
auto pos = map.find({ x, y });
cout << (pos != map.end() ? 'X' : ' ');
}
cout << '\n';
}
cout << endl;
}
*/
long
count(const vector<tuple<pos_type, velo_type>>& robots, long width, long height)
{
map<pos_type, long> map;
const auto width_half = width / 2;
const auto height_half = height / 2;
for ( const auto& [pos, velo]: robots ) {
const auto [x, y] = pos;
if ( x == width_half || y == height_half ) {
continue;
}
map[{ x / (width_half + 1), y / (height_half + 1) }]++;
}
long result = 1;
for ( const auto& [pos, count]: map ) {
result *= count;
}
return result;
}
void
move(vector<tuple<pos_type, velo_type>>& robots, long width, long height)
{
for ( auto& [pos, velo]: robots ) {
auto& [x, y] = pos;
auto [vx, vy] = velo;
x = (x + width + vx) % width;
y = (y + height + vy) % height;
}
}
void
part1(vector<tuple<pos_type, velo_type>> robots, long width, long height)
{
for ( long second = 0; second != 100; ++second ) {
move(robots, width, height);
}
cout << count(robots, width, height) << endl;
}
void
part2(vector<tuple<pos_type, velo_type>> robots, long width, long height)
{
auto min_result = numeric_limits<long>::max();
long second_found = 0;
for ( long second = 0; second != 100000; ++second ) {
auto result = count(robots, width, height);
if ( result < min_result ) {
second_found = second;
min_result = result;
}
move(robots, width, height);
}
cout << second_found << endl;
}
void
part2_alternative(vector<tuple<pos_type, velo_type>> robots, long width, long height)
{
set<pos_type> seen;
for ( long second = 0; second != 100000; ++second ) {
seen.clear();
bool overlap = false;
for ( const auto& [pos, velo]: robots ) {
if ( seen.contains(pos) ) {
overlap = true;
break;
}
seen.insert(pos);
}
if ( !overlap ) {
cout << second << endl;
break;
}
move(robots, width, height);
}
}
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 } };
}
size_t
flood_fill(const vector<tuple<pos_type, velo_type>>& robots)
{
set<pos_type> positions;
for ( const auto& [pos, velo]: robots ) {
positions.insert(pos);
}
size_t max_seen = 0;
for ( const auto& start: positions ) {
set<pos_type> seen;
queue<pos_type> queue;
queue.push(start);
while ( !queue.empty() ) {
auto pos = queue.front();
queue.pop();
if ( seen.contains(pos) ) {
continue;
}
seen.insert(pos);
for ( const auto& neighbor: neighbors(pos) ) {
if ( positions.contains(neighbor) ) {
queue.push(neighbor);
}
}
}
max_seen = max(max_seen, seen.size());
}
return max_seen;
}
void
part2_flood_fill(vector<tuple<pos_type, velo_type>> robots, long width, long height)
{
size_t max_count = 0;
long second_found = 0;
for ( long second = 0; second != 100000; ++second ) {
auto count = flood_fill(robots);
if ( count > max_count ) {
max_count = count;
second_found = second;
}
move(robots, width, height);
}
cout << second_found << endl;
}
int
main()
{
#if 0
auto robots = read_file("data/day14-sample1.txt");
part1(robots, 11, 7);
#else
auto robots = read_file("data/day14.txt");
part1(robots, 101, 103);
part2(robots, 101, 103);
part2_alternative(robots, 101, 103);
part2_flood_fill(robots, 101, 103);
#endif
}
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