1 files changed, 188 insertions, 0 deletions

diff --git a/2016/src/day12.cpp b/2016/src/day12.cpp
new file mode 100644
index 0000000..1e231a5
--- /dev/null
+++ b/2016/src/day12.cpp
@@ -0,0 +1,188 @@
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <optional>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+enum class OpCode : uint8_t {
+        CPY_VAL,
+        CPY_REG,
+        INC,
+        DEC,
+        JMP,
+        JNZ,
+};
+
+struct Instruction {
+        Instruction(OpCode opCode, char reg)
+            : opCode{ opCode }
+            , reg{ reg }
+        {
+        }
+
+        Instruction(OpCode opCode, int val)
+            : opCode{ opCode }
+            , val{ val }
+        {
+        }
+
+        Instruction(OpCode opCode, char reg, int val)
+            : opCode{ opCode }
+            , reg{ reg }
+            , val{ val }
+        {
+        }
+
+        OpCode         opCode;
+        optional<char> reg;
+        optional<int>  val;
+};
+
+/*
+ostream&
+operator<<(ostream& os, const Instruction& instruction)
+{
+    cout << (int) instruction.opCode << ":";
+    if ( instruction.reg.has_value() ) {
+        cout << " reg: " << instruction.reg.value();
+    }
+    if ( instruction.val.has_value() ) {
+        cout << " val: " << instruction.val.value();
+    }
+    return os;
+}
+*/
+
+vector<Instruction>
+read_file(const filesystem::path& filename)
+{
+        ifstream input{ filename };
+
+        vector<Instruction> instructions;
+
+        for ( string line; getline(input, line); ) {
+                if ( line.starts_with("cpy") ) {
+                        if ( isalpha(line.at(4)) != 0 ) {
+                                auto from_reg = line.at(4);
+                                auto to_reg   = line.at(6);
+                                instructions.emplace_back(OpCode::CPY_REG, to_reg, from_reg);
+                        }
+                        else {
+                                auto val = stoi(&line.at(strlen("cpy ")));
+                                auto reg = line.back();
+                                instructions.emplace_back(OpCode::CPY_VAL, reg, val);
+                        }
+                }
+                else if ( line.starts_with("inc") ) {
+                        auto reg = line.at(4);
+                        instructions.emplace_back(OpCode::INC, reg);
+                }
+                else if ( line.starts_with("dec") ) {
+                        auto reg = line.at(4);
+                        instructions.emplace_back(OpCode::DEC, reg);
+                }
+                else if ( line.starts_with("jnz 1") ) { // always jump!, WTF??
+                        auto off = stoi(&line.at(strlen("jnz 1 ")));
+                        instructions.emplace_back(OpCode::JMP, off);
+                }
+                else if ( line.starts_with("jnz") ) {
+                        auto reg = line.at(4);
+                        auto off = stoi(&line.at(strlen("jnz a ")));
+                        instructions.emplace_back(OpCode::JNZ, reg, off);
+                }
+                else {
+                        cerr << "unknown opcode..." << '\n';
+                }
+
+                // cout << line << " -> " << instructions.back() << '\n';
+        }
+
+        return instructions;
+}
+
+void
+execute(map<char, int>& memory, const vector<Instruction>& instructions)
+{
+        for ( size_t ip = 0; ip < instructions.size(); ) {
+                auto instruction = instructions.at(ip);
+
+                // cout << "#" << ip << " - " << memory['a'] << ", " << memory['b'] << ", " << memory['c'] << ", " << memory['d'] << ": " << (int) instruction.opCode << '\n';
+
+                switch ( instruction.opCode ) {
+                        using enum OpCode;
+                case CPY_VAL:
+                        memory[instruction.reg.value()] = instruction.val.value();
+                        ++ip;
+                        break;
+                case CPY_REG:
+                        memory[instruction.reg.value()] = memory[static_cast<char>(instruction.val.value())];
+                        ++ip;
+                        break;
+                case INC:
+                        memory[instruction.reg.value()]++;
+                        ++ip;
+                        break;
+                case DEC:
+                        memory[instruction.reg.value()]--;
+                        ++ip;
+                        break;
+                case JMP:
+                        ip += static_cast<size_t>(instruction.val.value());
+                        break;
+                case JNZ:
+                        if ( memory[instruction.reg.value()] != 0 ) {
+                                ip += static_cast<size_t>(instruction.val.value());
+                        }
+                        else {
+                                ++ip;
+                        }
+                        break;
+                }
+        }
+}
+
+void
+part1(const vector<Instruction>& instructions)
+{
+        map<char, int> memory;
+
+        memory['a'] = 0;
+        memory['b'] = 0;
+        memory['c'] = 0;
+        memory['d'] = 0;
+
+        execute(memory, instructions);
+
+        cout << "Part1: " << memory['a'] << '\n';
+}
+
+void
+part2(const vector<Instruction>& instructions)
+{
+        map<char, int> memory;
+
+        memory['a'] = 0;
+        memory['b'] = 0;
+        memory['c'] = 1;
+        memory['d'] = 0;
+
+        execute(memory, instructions);
+
+        cout << "Part2: " << memory['a'] << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+        const auto instructions = read_file("data/day12.txt");
+        part1(instructions);
+        part2(instructions);
+}