diff --git a/2017/11.cpp b/2017/11.cpp
index 0ffec6e..d879964 100644
--- a/2017/11.cpp
+++ b/2017/11.cpp
@@ -10,43 +10,12 @@
 
 #include <aocpp/Startup.hpp>
 #include <aocpp/Parsing.hpp>
+#include <aocpp/Hex.hpp>
+
+using namespace aocpp;
 
 namespace {
 
-/*
-  \ n  /
-nw +--+ ne
-  /    \
--+      +-
-  \    /
-sw +--+ se
-  / s  \
-*/
-
-struct Hex {
-  std::int64_t q, r, s;
-};
-
-constexpr Hex HEX_N  {  0, -1,  1 };
-constexpr Hex HEX_NE {  1, -1,  0 };
-constexpr Hex HEX_SE {  1,  0, -1 };
-constexpr Hex HEX_S  {  0,  1, -1 };
-constexpr Hex HEX_SW { -1,  1,  0 };
-constexpr Hex HEX_NW { -1,  0,  1 };
-
-auto operator+(Hex a, Hex b) -> Hex {
-  return {a.q + b.q, a.r + b.r, a.s + b.s };
-}
-
-auto operator+=(Hex & a, Hex b) -> Hex & {
-  a.q += b.q; a.r += b.r; a.s += b.s;
-  return a;
-}
-
-auto hex_distance(Hex hex) -> std::int64_t {
-  return (std::abs(hex.q) + std::abs(hex.r) + std::abs(hex.s)) / 2;
-}
-
 auto Walk(std::string const& commands)
 -> std::pair<std::int64_t, std::int64_t>
 {
@@ -93,7 +62,7 @@ TEST_SUITE("2017-11 examples") {
 
 auto main(int argc, char** argv) -> int {
   std::string line;
-  std::getline(*aocpp::Startup(argc, argv), line);
+  std::getline(*Startup(argc, argv), line);
   auto [part1, part2] = Walk(line);
   std::cout << "Part 1: " << part1 << std::endl;
   std::cout << "Part 2: " << part2 << std::endl;
diff --git a/2017/12.cpp b/2017/12.cpp
new file mode 100644
index 0000000..54c83ef
--- /dev/null
+++ b/2017/12.cpp
@@ -0,0 +1,109 @@
+#include <cstdint>
+#include <iostream>
+#include <sstream>
+#include <string>
+#include <vector>
+#include <tuple>
+
+#include <doctest.h>
+
+#include <aocpp/Startup.hpp>
+
+using namespace aocpp;
+
+namespace {
+
+auto Parse(std::istream & in)
+-> std::vector<std::vector<std::uint16_t>>
+{
+  std::string line;
+  std::vector<std::vector<std::uint16_t>> result;
+  while (std::getline(in, line)) {
+    line.erase(std::remove_if(line.begin(), line.end(), [](auto c) {
+      return c=='<' || c=='-' || c=='>' || c == ',';
+    }), line.end());
+    std::istringstream lin { line };
+    std::uint16_t x;
+    lin >> x;
+    std::vector<std::uint16_t> links;
+    while (lin >> x) {
+      links.push_back(x);
+    }
+    result.emplace_back(std::move(links));
+  }
+  return result;
+}
+
+auto Find(std::vector<std::uint16_t> & leaders, std::uint16_t const who) -> std::uint16_t
+{
+  std::uint16_t cursor;
+  std::uint16_t leader = who;
+
+  do {
+    cursor = leader;
+    leader = leaders[cursor];
+  } while (leader != cursor);
+
+  cursor = who;
+  while (cursor != leader) {
+    auto tmp = leaders[cursor];
+    leaders[cursor] = leader;
+    cursor = tmp;
+  }
+
+  return leader;
+}
+
+auto LinkNodes(std::vector<std::vector<std::uint16_t>> const& input)
+-> std::pair<std::size_t, std::size_t>
+{
+  // Allocate leaders array and assign each node as its own leader
+  std::vector<std::uint16_t> leaders(input.size());
+  for (std::size_t i = 0; i < leaders.size(); i++) {
+    leaders[i] = i;
+  }
+
+  // Link up all the nodes as specified in the input file
+  for (std::size_t i = 0; i < input.size(); i++) {
+    auto x_ = Find(leaders, i);
+    for (auto const y : input[i]) {
+      leaders[Find(leaders,y)] = x_;
+    }
+  }
+
+  std::size_t part1 = 0;
+  std::size_t part2 = 0;
+
+  auto target1 = Find(leaders, 0);
+  for (std::size_t i = 0; i < leaders.size(); i++) {
+    if (Find(leaders, i) == target1) part1++;
+    if (leaders[i] == i) part2++;
+  }
+
+  return {part1, part2};
+}
+
+} // namespace
+
+TEST_SUITE("2017-12 examples") {
+  TEST_CASE("example") {
+    std::istringstream in {
+      "0 <-> 2\n"
+      "1 <-> 1\n"
+      "2 <-> 0, 3, 4\n"
+      "3 <-> 2, 4\n"
+      "4 <-> 2, 3, 6\n"
+      "5 <-> 6\n"
+      "6 <-> 4, 5\n"};
+    auto [p1,p2] = LinkNodes(Parse(in));
+    CHECK(p1 == 6);
+    CHECK(p2 == 2);
+  }
+}
+
+auto main(int argc, char** argv) -> int {
+  auto input = Parse(*Startup(argc, argv));
+  auto [part1, part2] = LinkNodes(input);
+  std::cout << "Part 1: " << part1 << std::endl;
+  std::cout << "Part 2: " << part2 << std::endl;
+}
\ No newline at end of file
diff --git a/2017/CMakeLists.txt b/2017/CMakeLists.txt
index 7ee3bc3..cbd2fb4 100644
--- a/2017/CMakeLists.txt
+++ b/2017/CMakeLists.txt
@@ -10,6 +10,9 @@ target_link_libraries(2017_10 aocpp knothash)
 add_executable(2017_11 11.cpp)
 target_link_libraries(2017_11 aocpp)
 
+add_executable(2017_12 12.cpp)
+target_link_libraries(2017_12 aocpp)
+
 add_executable(2017_14 14.cpp)
 target_link_libraries(2017_14 aocpp knothash)
 
diff --git a/lib/include/aocpp/Hex.hpp b/lib/include/aocpp/Hex.hpp
new file mode 100644
index 0000000..0127c11
--- /dev/null
+++ b/lib/include/aocpp/Hex.hpp
@@ -0,0 +1,57 @@
+#ifndef AOCPP_HEX_HPP_
+#define AOCPP_HEX_HPP_
+
+#include <numeric>
+#include <cstdint>
+
+namespace aocpp {
+/*
+  \ n  /
+nw +--+ ne
+  /    \
+-+      +-
+  \    /
+sw +--+ se
+  / s  \
+*/
+
+struct Hex {
+  std::int64_t q, r, s;
+};
+
+constexpr Hex HEX_N  {  0, -1,  1 };
+constexpr Hex HEX_NE {  1, -1,  0 };
+constexpr Hex HEX_SE {  1,  0, -1 };
+constexpr Hex HEX_S  {  0,  1, -1 };
+constexpr Hex HEX_SW { -1,  1,  0 };
+constexpr Hex HEX_NW { -1,  0,  1 };
+
+auto operator+(Hex const& a, Hex const& b) -> Hex {
+  return {a.q + b.q, a.r + b.r, a.s + b.s };
+}
+
+auto operator+=(Hex & a, Hex const& b) -> Hex & {
+  a.q += b.q; a.r += b.r; a.s += b.s;
+  return a;
+}
+
+auto operator-(Hex const& a, Hex const& b) -> Hex {
+  return {a.q - b.q, a.r - b.r, a.s - b.s };
+}
+
+auto operator-=(Hex & a, Hex const& b) -> Hex & {
+  a.q -= b.q; a.r -= b.r; a.s -= b.s;
+  return a;
+}
+
+auto operator-(Hex const& a) -> Hex {
+  return {-a.q, -a.r, -a.s };
+}
+
+auto hex_distance(Hex hex) -> std::int64_t {
+  return (std::abs(hex.q) + std::abs(hex.r) + std::abs(hex.s)) / 2;
+}
+
+} // namespace
+
+#endif
\ No newline at end of file