diff --git a/2022/18.cpp b/2022/18.cpp
new file mode 100644
index 0000000..ea046c3
--- /dev/null
+++ b/2022/18.cpp
@@ -0,0 +1,104 @@
+#include <algorithm>
+#include <concepts>
+#include <cstdint>
+#include <iostream>
+#include <set>
+#include <sstream>
+#include <stdexcept>
+#include <string>
+#include <tuple>
+#include <utility>
+#include <vector>
+
+#include <doctest.h>
+
+#include <aocpp/Startup.hpp>
+#include <aocpp/Vec.hpp>
+
+namespace {
+
+using Coord = aocpp::Vec<std::int64_t, 3>;
+
+/// @brief Parse an input stream
+/// @param in white-space delimited, comma-separated coordinates
+/// @return set of coordinates
+auto Parse(std::istream & in) -> std::set<Coord>
+{
+  std::set<Coord> result;
+  std::string line;
+  while (in >> line) {
+    Coord x;
+    if (3 != std::sscanf(line.c_str(), "%lld,%lld,%lld\n", &x[0], &x[1], &x[2]))
+      throw std::runtime_error{"bad input line"};
+    result.insert(x);
+  }
+  return result;
+}
+
+auto Part1(std::set<Coord> const& obj) -> std::size_t
+{
+  std::size_t result {0};
+  for (auto && x : obj) {
+    x.EachNeighbor([&](Coord const& y) {
+      if (!obj.contains(y)) result++;
+    });
+  }
+  return result;
+}
+
+auto Part2(std::set<Coord> const& obj) -> std::size_t
+{
+  auto [lo, hi] = Coord::BoundingBox(obj.begin(), obj.end());
+  lo -= Coord(1);
+  hi += Coord(1);
+
+  std::set<Coord> seen {lo};
+  std::vector<Coord> work {lo};
+  std::size_t result {0};
+
+  while (!work.empty()) {
+    auto x = work.back();
+    work.pop_back();
+    x.EachNeighbor([&, lo=lo, hi=hi](Coord const& y) {
+      if (obj.contains(y)) {
+        result++;
+      } else if (y.InRange(lo, hi) && seen.insert(y).second) {
+        work.push_back(y);
+      }
+    });
+  }
+
+  return result;
+}
+
+} // namespace
+
+TEST_SUITE("2022-12 examples") {
+  TEST_CASE("documented example") {
+    std::istringstream in {
+      "2,2,2\n"
+      "1,2,2\n"
+      "3,2,2\n"
+      "2,1,2\n"
+      "2,3,2\n"
+      "2,2,1\n"
+      "2,2,3\n"
+      "2,2,4\n"
+      "2,2,6\n"
+      "1,2,5\n"
+      "3,2,5\n"
+      "2,1,5\n"
+      "2,3,5\n"
+    };
+    auto obj = Parse(in);
+    CHECK(64 == Part1(obj));
+    CHECK(58 == Part2(obj));
+  }
+}
+
+auto main(int argc, char** argv) -> int
+{
+  auto obj = Parse(*aocpp::Startup(argc, argv));
+  std::cout << "Part 1: " << Part1(obj) << std::endl;
+  std::cout << "Part 2: " << Part2(obj) << std::endl;
+}
diff --git a/2022/CMakeLists.txt b/2022/CMakeLists.txt
index 76613ed..9e8cbb9 100644
--- a/2022/CMakeLists.txt
+++ b/2022/CMakeLists.txt
@@ -10,5 +10,8 @@ target_link_libraries(2022_04 aocpp)
 add_executable(2022_12 12.cpp)
 target_link_libraries(2022_12 aocpp)
 
+add_executable(2022_18 18.cpp)
+target_link_libraries(2022_18 aocpp)
+
 add_executable(2022_25 25.cpp)
 target_link_libraries(2022_25 aocpp)
diff --git a/lib/include/aocpp/Vec.hpp b/lib/include/aocpp/Vec.hpp
new file mode 100644
index 0000000..82e338f
--- /dev/null
+++ b/lib/include/aocpp/Vec.hpp
@@ -0,0 +1,143 @@
+#ifndef AOCPP_VEC_HPP_
+#define AOCPP_VEC_HPP_
+
+#include <array>
+#include <cstdint>
+#include <iostream>
+#include <tuple>
+#include <assert.h>
+
+namespace aocpp {
+
+template <typename T, std::size_t N>
+class Vec {
+  T arr[N];
+
+  auto range_check(std::size_t i) -> void {
+    if (i >= N) {
+      throw std::out_of_range{std::to_string(i) + " >= " + std::to_string(N)};
+    }
+  }
+
+public:
+  Vec() = default;
+  auto operator<=>(const Vec&) const = default;
+
+  explicit Vec(T x) {
+    std::fill_n(arr, N, x);
+  }
+
+  Vec(std::initializer_list<T> xs) {
+    assert(N == xs.size());
+    std::move(xs.begin(), xs.end(), arr);
+  }
+
+  auto operator[](std::size_t i) const -> T {
+    return arr[i];
+  }
+  
+  auto operator[](std::size_t i) -> T & {
+    return arr[i];
+  }
+
+  auto at(std::size_t i) const -> T {
+    range_check(i);
+    return arr[i];
+  }
+  
+  auto at(std::size_t i) -> T & {
+    range_check(i);
+    return arr[i];
+  }
+
+  auto operator+(Vec const& rhs) const -> Vec
+  {
+    Vec result;
+    for (std::size_t i = 0; i < N; ++i) result[i] = arr[i] + rhs[i];
+    return result;
+  }
+
+  auto operator-(Vec const& rhs) const -> Vec {
+    Vec result;
+    for (std::size_t i = 0; i < N; ++i) result[i] = arr[i] - rhs[i];
+    return result;
+  }
+
+  auto operator-() const -> Vec {
+    Vec result;
+    for (std::size_t i = 0; i < N; ++i) result[i] = -arr[i];
+    return result;
+  }
+
+  auto operator+=(Vec const& rhs) -> Vec & {
+    for (std::size_t i = 0; i < N; ++i) arr[i] += rhs[i];
+    return *this;
+  }
+
+  auto operator-=(Vec const& rhs) -> Vec &
+  {
+    for (std::size_t i = 0; i < N; ++i) arr[i] -= rhs[i];
+    return *this;
+  }
+
+  /// @brief Check inclusion in a cuboid
+  /// @param lo lower-corner
+  /// @param hi upper-corner
+  /// @return this point is contained in the cuboid
+  auto InRange(Vec const& lo, Vec const& hi) const -> bool
+  {
+    for (std::size_t i = 0; i < N; ++i) {
+      if (arr[i] < lo[i] || hi[i] < arr[i]) return false;
+    }
+    return true;
+  }
+
+  /// @brief Find the corners of the smallest cuboid containing all the given points.
+  /// @tparam It InputIterator
+  /// @param first beginning of input range
+  /// @param last end of input range
+  /// @return pair of lower and upper cuboid corners
+  template <typename It>
+  static auto BoundingBox(It first, It last) -> std::pair<Vec, Vec>
+  {
+    Vec lo(0), hi(0);
+    std::for_each(first, last, [&](auto const& x) {
+      for (std::size_t i = 0; i < N; ++i) {
+        if (lo[i] > x[i]) lo[i] = x[i];
+        if (hi[i] < x[i]) hi[i] = x[i];
+      }
+    });
+    return {lo, hi};
+  }
+
+  /// @brief Apply a continuation to each neighbor of a vector
+  /// @param k continuation applied to cardinal direction neighbors
+  auto EachNeighbor(std::invocable<Vec const&> auto k) const -> void
+  {
+    auto x = *this;
+    for (std::size_t i = 0; i < N; ++i) {
+      x[i] += 1;
+      k(std::as_const(x));
+      x[i] -= 2;
+      k(std::as_const(x));
+      x[i] += 1;
+    }
+  }
+};
+
+template <typename T, std::size_t N>
+auto operator<<(std::ostream & out, Vec<T,N> const& rhs) -> std::ostream &
+{
+  out << "{";
+  if (0 < N) {
+    out << rhs[0];
+  }
+  for (std::size_t i = 1; i < N; ++i) {
+    out << "," << rhs[i];
+  }
+  return out << "}";
+}
+
+}
+
+#endif