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#include <charconv>
#include <filesystem>
#include <fstream>
#include <iostream>
#include <map>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
namespace {
template<typename T>
struct CPU {
[[nodiscard]]
T get(const string& ref)
{
T value{};
auto [ptr, ec] = from_chars(ref.data(), ref.data() + ref.size(), value);
if ( ec == errc() ) {
return value;
}
return memory[ref];
}
void set(const string& ref, T value)
{
memory[ref] = value;
}
void sub(const string& ref, T value)
{
memory[ref] -= value;
}
void mul(const string& ref, T value)
{
memory[ref] *= value;
}
T execute(const vector<vector<string>>& code)
{
int mul_executed = 0;
for ( size_t ip = 0; ip < code.size(); ++ip ) {
const auto& line = code.at(ip);
const auto& opcode = line.at(0);
if ( opcode == "set" ) {
set(line.at(1), get(line.at(2)));
}
else if ( opcode == "sub" ) {
sub(line.at(1), get(line.at(2)));
}
else if ( opcode == "mul" ) {
++mul_executed;
mul(line.at(1), get(line.at(2)));
}
else if ( opcode == "jnz" ) {
auto value = get(line.at(1));
if ( value != 0 ) {
auto offset = get(line.at(2));
ip += static_cast<size_t>(offset - 1);
}
}
else {
cerr << "unknown opcode: " << opcode << '\n';
return -1;
}
}
return mul_executed;
}
map<string, T> memory;
};
vector<string>
split(const string& line)
{
stringstream strm{ line };
vector<string> data;
for ( string line; strm >> line; ) {
data.emplace_back(line);
}
return data;
}
vector<vector<string>>
read_file(const filesystem::path& filename)
{
ifstream file{ filename };
vector<vector<string>> data;
for ( string line; getline(file, line); ) {
const auto parts = split(line);
data.emplace_back(parts);
}
return data;
}
void
part1(const vector<vector<string>>& code)
{
CPU<long> cpu{};
cout << "Part1: " << cpu.execute(code) << '\n';
}
void
part2(const vector<vector<string>>& code)
{
CPU<long> cpu{};
cpu.memory["a"] = 1;
// execute only initialization code
cpu.execute({ code.begin(), code.begin() + 8 });
auto b_start = cpu.memory["b"];
auto c_end = cpu.memory["c"];
auto is_prime = [](long n) {
if ( n < 2 ) {
return false;
}
for ( long i = 2; i * i <= n; ++i ) {
if ( n % i == 0 ) {
return false;
}
}
return true;
};
const long step = 17;
long memory_h = 0;
for ( long b = b_start; b <= c_end; b += step ) {
if ( !is_prime(b) ) {
++memory_h;
}
}
cout << "Part2: " << memory_h << '\n';
}
} // namespace
int
main()
{
auto instr = read_file("data/day23.txt");
part1(instr);
part2(instr);
}
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