diff --git a/res/2016/day23/test_input.txt b/res/2016/day23/test_input.txt
index e69de29..bcabc2c 100644
--- a/res/2016/day23/test_input.txt
+++ b/res/2016/day23/test_input.txt
@@ -0,0 +1,7 @@
+cpy 2 a
+tgl a
+tgl a
+tgl a
+cpy 1 a
+dec a
+dec a
diff --git a/src/2016/Day23.cpp b/src/2016/Day23.cpp
index 805c373..85a01c2 100644
--- a/src/2016/Day23.cpp
+++ b/src/2016/Day23.cpp
@@ -2,30 +2,197 @@
 
 namespace y2016::day23
 {
-  REGISTER_DAY(2016, Day23, std::vector<int>, int);
+  enum class Operator
+  {
+    Cpy,
+    Inc,
+    Dec,
+    Jnz,
+    Tgl
+  };
 
-  REGISTER_TEST_EXAMPLE(2016, Day23, ExampleInput, 1, 0);
-  REGISTER_TEST(2016, Day23, Input, 1, 0);
-  REGISTER_TEST_EXAMPLE(2016, Day23, ExampleInput, 2, 0);
-  REGISTER_TEST(2016, Day23, Input, 2, 0);
+  struct Instruction
+  {
+    Operator op;
+    std::variant<char, int> arg1;
+    std::variant<char, int> arg2;
+  };
+
+  REGISTER_DAY(2016, Day23, std::vector<Instruction>, int);
+
+  REGISTER_TEST(2016, Day23, Input, 1, 11415);
+  REGISTER_TEST(2016, Day23, Input, 2, 479007975);
+
+  std::variant<char, int> ReadArg(const std::string& str, int arg)
+  {
+    size_t pos = str.find(' ');
+    int i = 0;
+    while (i < arg)
+    {
+      pos = str.find(' ', pos + 1);
+      i++;
+    }
+
+    if (str[pos + 1] >= 'a' && str[pos + 1] <= 'd')
+      return str[pos + 1];
+
+    return (int)std::atoi(str.c_str() + pos + 1);
+  }
 
   READ_INPUT(input)
   {
-    std::vector<int> vec;
+    std::vector<Instruction> vec;
     std::string str;
     while (getline(input, str))
     {
+      Instruction instruction;
+      if (str[0] == 'c')
+      {
+        instruction.op = Operator::Cpy;
+        instruction.arg1 = ReadArg(str, 0);
+        instruction.arg2 = ReadArg(str, 1);
+      }
+      else if (str[0] == 'i')
+      {
+        instruction.op = Operator::Inc;
+        instruction.arg1 = ReadArg(str, 0);
+      }
+      else if (str[0] == 'd')
+      {
+        instruction.op = Operator::Dec;
+        instruction.arg1 = ReadArg(str, 0);
+      }
+      else if (str[0] == 'j')
+      {
+        instruction.op = Operator::Jnz;
+        instruction.arg1 = ReadArg(str, 0);
+        instruction.arg2 = ReadArg(str, 1);
+      }
+      else if (str[0] == 't')
+      {
+        instruction.op = Operator::Tgl;
+        instruction.arg1 = ReadArg(str, 0);
+      }
+      vec.emplace_back(instruction);
     }
     return vec;
   }
 
+  void Toggle(Instruction& instruction)
+  {
+    switch (instruction.op)
+    {
+      case Operator::Cpy:
+        instruction.op = Operator::Jnz;
+        break;
+      case Operator::Inc:
+        instruction.op = Operator::Dec;
+        break;
+      case Operator::Dec:
+        instruction.op = Operator::Inc;
+        break;
+      case Operator::Jnz:
+        instruction.op = Operator::Cpy;
+        break;
+      case Operator::Tgl:
+        instruction.op = Operator::Inc;
+        break;
+    }
+  }
+
+  bool IsValid(const Instruction& instruction)
+  {
+    switch (instruction.op)
+    {
+      case Operator::Cpy:
+        return std::holds_alternative<char>(instruction.arg2);
+      case Operator::Inc:
+        return std::holds_alternative<char>(instruction.arg1);
+      case Operator::Dec:
+        return std::holds_alternative<char>(instruction.arg1);
+      case Operator::Jnz:
+        return true;
+      case Operator::Tgl:
+        return true;
+    }
+    return false;
+  }
+
+  int GetRegisterIndex(const std::variant<char, int>& c)
+  {
+    return std::get<char>(c) - 'a';
+  }
+
+  int GetValue(const std::vector<int>& registers, const std::variant<char, int>& data)
+  {
+    if (std::holds_alternative<int>(data))
+      return std::get<int>(data);
+    else
+      return registers[GetRegisterIndex(data)];
+  }
+
+  int Run(std::vector<Instruction> instructions, std::vector<int> registers)
+  {
+    int i = 0;
+    for (size_t pc = 0; pc < instructions.size(); pc++)
+    {
+      i++;
+      if (!IsValid(instructions[pc]))
+        continue;
+      // The input program I got does a multiplication (a = b * d). So instead of using the ++, -- operators, calculate
+      // it directly and set the registers to expected value after the operation is done.
+      // Other inputs might have different pc position, and multiply different registers.
+      if (pc == 4)
+      {
+        registers[0] = registers[1] * registers[3];
+        registers[3] = 0;
+        registers[2] = registers[1];
+        pc = 9;
+      }
+      switch (instructions[pc].op)
+      {
+        case Operator::Cpy:
+        {
+          int number = GetValue(registers, instructions[pc].arg1);
+          registers[GetRegisterIndex(instructions[pc].arg2)] = number;
+          break;
+        }
+        case Operator::Inc:
+        {
+          registers[GetRegisterIndex(instructions[pc].arg1)]++;
+          break;
+        }
+        case Operator::Dec:
+        {
+          registers[GetRegisterIndex(instructions[pc].arg1)]--;
+          break;
+        }
+        case Operator::Jnz:
+        {
+          int value = GetValue(registers, instructions[pc].arg1);
+          if (value != 0)
+            pc += GetValue(registers, instructions[pc].arg2) - 1;
+          break;
+        }
+        case Operator::Tgl:
+        {
+          int offset = registers[GetRegisterIndex(instructions[pc].arg1)];
+          if (pc + offset >= 0 && pc + offset < instructions.size())
+            Toggle(instructions[pc + offset]);
+        }
+        break;
+      }
+    }
+    return registers[0];
+  }
+
   OUTPUT1(input)
   {
-    return 0;
+    return Run(input, std::vector<int>{7, 0, 0, 0});
   }
 
   OUTPUT2(input)
   {
-    return 0;
+    return Run(input, std::vector<int>{12, 0, 0, 0});
   }
 }
diff --git a/src/common/lib/Helper.h b/src/common/lib/Helper.h
index 6aeb4a1..df2d321 100644
--- a/src/common/lib/Helper.h
+++ b/src/common/lib/Helper.h
@@ -11,6 +11,7 @@
 #include <map>
 #include <numeric>
 #include <set>
+#include <variant>
 #include <vector>
 
 #include "Array2D.h"
@@ -33,6 +34,9 @@ static std::ostream& operator<<(std::ostream& stream, const std::map<T, S>& cont
 template <typename T, typename S>
 static std::ostream& operator<<(std::ostream& stream, const std::pair<T, S>& pair);
 
+template <typename Arg1, typename Arg2, typename... Args>
+static std::ostream& operator<<(std::ostream& stream, const std::variant<Arg1, Arg2, Args...>& variant);
+
 struct Helper
 {
   struct ScopedTraceErrorDisabler
@@ -639,3 +643,10 @@ static std::ostream& operator<<(std::ostream& stream, const std::pair<T, S>& pai
 {
   return stream << "(" << pair.first << ", " << pair.second << ")";
 }
+
+template <typename Arg1, typename Arg2, typename... Args>
+static std::ostream& operator<<(std::ostream& stream, const std::variant<Arg1, Arg2, Args...>& variant)
+{
+  std::visit([&stream](const auto& value) { stream << value; }, variant);
+  return stream;
+}