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#include <fstream>
#include <functional>
#include <iostream>
#include <map>
#include <regex>
#include <string>
#include <vector>
using namespace std;
string
read_file(string_view filename)
{
fstream input{ filename };
return { istreambuf_iterator<char>{ input }, istreambuf_iterator<char>{} };
}
vector<string>
split(string_view line, string_view delimiter)
{
size_t pos_start = 0;
size_t pos_end = 0;
vector<string> res;
while ( (pos_end = line.find(delimiter, pos_start)) != string::npos ) {
auto token = line.substr(pos_start, pos_end - pos_start);
pos_start = pos_end + delimiter.length();
res.emplace_back(token);
}
if ( pos_start != line.size() ) {
res.emplace_back(line.substr(pos_start));
}
return res;
}
void
part1(map<string, tuple<vector<tuple<string, string, long, string>>, string>> rules, const vector<string>& parts)
{
long sum = 0;
for ( const auto& part: parts ) {
static const regex parts_pattern{ R"(\{x=(\d*),m=(\d*),a=(\d*),s=(\d*)\})" };
smatch smatch;
if ( !regex_search(part, smatch, parts_pattern) ) {
continue;
}
map<string, long> values = {
{ "x", stol(smatch[1]) },
{ "m", stol(smatch[2]) },
{ "a", stol(smatch[3]) },
{ "s", stol(smatch[4]) },
};
string rule = "in";
while ( rule != "A" && rule != "R" ) {
auto [sub_rules, next_rule] = rules[rule];
for ( const auto& sub_rule: sub_rules ) {
const auto [field, cmp, value, dest] = sub_rule;
if ( values.contains(field) && ((cmp == ">" && values[field] > value) || (cmp == "<" && values[field] < value)) ) {
next_rule = dest;
break;
}
}
rule = next_rule;
}
if ( rule == "A" ) {
sum += values["x"];
sum += values["m"];
sum += values["a"];
sum += values["s"];
}
}
cout << sum << endl;
}
void
part2(map<string, tuple<vector<tuple<string, string, long, string>>, string>> rules)
{
function<long(map<string, tuple<long, long>>, string)> count = [&](map<string, tuple<long, long>> ranges, const string& name) -> long {
if ( name == "R" ) {
return 0;
}
if ( name == "A" ) {
long result = 1;
for ( const auto& range: ranges ) {
const auto [lo, hi] = range.second;
result *= hi - lo + 1;
}
return result;
}
const auto [sub_rules, fallback] = rules[name];
long result = 0;
for ( const auto& [key, cmp, value, target]: sub_rules ) {
auto sub_ranges = ranges;
auto [lo, hi] = ranges[key];
if ( cmp == "<" ) {
sub_ranges[key] = { lo, value - 1 };
ranges[key] = { value, hi };
}
else /* if ( cmp == ">" ) */ {
ranges[key] = { lo, value };
sub_ranges[key] = { value + 1, hi };
}
result += count(sub_ranges, target);
}
result += count(ranges, fallback);
return result;
};
cout << count({
{ "x", { 1, 4000 } },
{ "m", { 1, 4000 } },
{ "a", { 1, 4000 } },
{ "s", { 1, 4000 } },
},
"in")
<< endl;
}
int
main()
{
const auto input = split(read_file("data/day19.txt"), "\n\n");
const auto rules_string = split(input[0], "\n");
const auto parts = split(input[1], "\n");
map<string, tuple<vector<tuple<string, string, long, string>>, string>> rules;
for ( const auto& rule: rules_string ) {
static const regex rules_pattern{ R"((.*)\{(.*),(.*)\})" };
smatch smatch;
if ( !regex_search(rule, smatch, rules_pattern) ) {
continue;
}
string name = smatch[1];
string default_rule = smatch[3];
vector<tuple<string, string, long, string>> sub_rules;
for ( const auto& sub_rule: split(smatch[2].str(), ",") ) {
static const regex sub_rules_pattern{ R"((.)(.)(\d*):(.*))" };
std::smatch smatch2;
if ( regex_search(sub_rule, smatch2, sub_rules_pattern) ) {
sub_rules.emplace_back(smatch2[1], smatch2[2], stol(smatch2[3]), smatch2[4]);
}
}
rules[name] = make_tuple(sub_rules, default_rule);
}
part1(rules, parts);
part2(rules);
}
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