diff --git a/res/2016/day04/test_input.txt b/res/2016/day04/test_input.txt
index e69de29..1d296af 100644
--- a/res/2016/day04/test_input.txt
+++ b/res/2016/day04/test_input.txt
@@ -0,0 +1,4 @@
+aaaaa-bbb-z-y-x-123[abxyz]
+a-b-c-d-e-f-g-h-987[abcde]
+not-a-real-room-404[oarel]
+totally-real-room-200[decoy]
diff --git a/src/2016/Day04.cpp b/src/2016/Day04.cpp
index d7a4de3..4799c0a 100644
--- a/src/2016/Day04.cpp
+++ b/src/2016/Day04.cpp
@@ -2,30 +2,108 @@
 
 namespace y2016::day04
 {
-  REGISTER_DAY(2016, Day04, std::vector<int>, int);
+  struct Room
+  {
+    std::string name;
+    int sectorId;
+    std::string checksum;
+  };
 
-  REGISTER_TEST_EXAMPLE(2016, Day04, ExampleInput, 1, 0);
-  REGISTER_TEST(2016, Day04, Input, 1, 0);
-  REGISTER_TEST_EXAMPLE(2016, Day04, ExampleInput, 2, 0);
-  REGISTER_TEST(2016, Day04, Input, 2, 0);
+  REGISTER_DAY(2016, Day04, std::vector<Room>, int);
+
+  REGISTER_TEST_EXAMPLE(2016, Day04, ExampleInput, 1, 1514);
+  REGISTER_TEST(2016, Day04, Input, 1, 278221);
+  REGISTER_TEST(2016, Day04, Input, 2, 267);
 
   READ_INPUT(input)
   {
-    std::vector<int> vec;
+    std::vector<Room> vec;
     std::string str;
     while (getline(input, str))
     {
+      Room room;
+      std::stringstream ss{str};
+
+      getline(ss, room.name, '[');
+      size_t pos = room.name.find_last_of('-');
+      room.sectorId = std::strtoll(room.name.c_str() + pos + 1, nullptr, 10);
+      room.name = room.name.substr(0, pos);
+
+      getline(ss, room.checksum, ']');
+      vec.emplace_back(room);
     }
     return vec;
   }
 
+  struct CharCount
+  {
+    char c;
+    int count;
+
+    bool operator<(const CharCount& rhs) const
+    {
+      if (count != rhs.count)
+        return count > rhs.count;
+      return c < rhs.c;
+    }
+  };
+
+  bool ValidRoom(const Room& room)
+  {
+    std::array<int, 'z' - 'a' + 1> counts;
+    counts.fill(0);
+    for (auto c : room.name)
+    {
+      if (c >= 'a' && c <= 'z')
+        counts[c - 'a']++;
+    }
+
+    std::set<CharCount> mostUsed;
+    for (int i = 0; i < counts.size(); i++)
+    {
+      if (counts[i] > 0)
+        mostUsed.emplace(CharCount{(char)('a' + i), counts[i]});
+    }
+
+    int i = 0;
+    for (auto it = mostUsed.begin(); i < 5; it++, i++)
+    {
+      if (room.checksum[i] != it->c)
+      {
+        return false;
+      }
+    }
+    return true;
+  }
+
   OUTPUT1(input)
   {
-    return 0;
+    int count = 0;
+    for (const auto& room : input)
+    {
+      if (ValidRoom(room))
+        count += room.sectorId;
+    }
+    return count;
   }
 
   OUTPUT2(input)
   {
+    for (const auto& room : input)
+    {
+      if (!ValidRoom(room))
+        continue;
+
+      std::string newName = room.name;
+      for (auto& c : newName)
+      {
+        if (c >= 'a' && c <= 'z')
+          c = ((c - 'a') + room.sectorId) % ('z' - 'a' + 1) + 'a';
+      }
+
+      if (newName == "northpole-object-storage")
+        return room.sectorId;
+    }
     return 0;
   }
 }
diff --git a/src/common/lib/Helper.h b/src/common/lib/Helper.h
index 19a529b..c4db010 100644
--- a/src/common/lib/Helper.h
+++ b/src/common/lib/Helper.h
@@ -18,11 +18,11 @@
 
 #define BIT(x) (1 << (x))
 
-template <typename T>
-static std::ostream& operator<<(std::ostream& stream, const std::vector<T>& container);
+template <typename... Args>
+static std::ostream& operator<<(std::ostream& stream, const std::vector<Args...>& container);
 
-template <typename T>
-static std::ostream& operator<<(std::ostream& stream, const std::set<T>& container);
+template <typename... Args>
+static std::ostream& operator<<(std::ostream& stream, const std::set<Args...>& container);
 
 template <typename T, typename S>
 static std::ostream& operator<<(std::ostream& stream, const std::map<T, S>& container);
@@ -730,14 +730,14 @@ public:
 
 inline bool Helper::traceErrors = true;
 
-template <typename T>
-static std::ostream& operator<<(std::ostream& stream, const std::vector<T>& container)
+template <typename... Args>
+static std::ostream& operator<<(std::ostream& stream, const std::vector<Args...>& container)
 {
   return Helper::Print(stream, container);
 }
 
-template <typename T>
-static std::ostream& operator<<(std::ostream& stream, const std::set<T>& container)
+template <typename... Args>
+static std::ostream& operator<<(std::ostream& stream, const std::set<Args...>& container)
 {
   return Helper::Print(stream, container);
 }