1 files changed, 158 insertions, 0 deletions

diff --git a/2017/src/day23.cpp b/2017/src/day23.cpp
new file mode 100644
index 0000000..1f4b960
--- /dev/null
+++ b/2017/src/day23.cpp
@@ -0,0 +1,158 @@
+#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);
+}