diff --git a/2022/13.cpp b/2022/13.cpp
new file mode 100644
index 0000000..0ca486c
--- /dev/null
+++ b/2022/13.cpp
@@ -0,0 +1,149 @@
+#include <cstdint>
+#include <iostream>
+#include <set>
+#include <sstream>
+#include <tuple>
+#include <vector>
+#include <variant>
+
+#include <doctest.h>
+
+#include <aocpp/Startup.hpp>
+
+namespace {
+
+struct Tree {
+  std::variant<std::int64_t, std::vector<Tree>> var;
+
+  auto operator<(Tree const& rhs) const -> bool {
+    if (var.index() == 0) {
+      if (rhs.var.index() == 0) {
+        return std::get<0>(var) < std::get<0>(rhs.var);
+      } else {
+        return Tree{std::vector{*this}} < rhs;
+      }
+    } else {
+      if (rhs.var.index() == 0) {
+        return *this < Tree{std::vector{rhs}};
+      } else {
+        return std::get<1>(var) < std::get<1>(rhs.var);
+      }
+    }
+  }
+};
+
+using Input = std::vector<Tree>;
+
+auto ParseTree(std::string::iterator & begin, std::string::iterator end) -> Tree
+{
+  if (*begin == '[') {
+    begin++;
+    if (*begin == ']') {
+      begin++;
+      return Tree{std::vector<Tree>{}};
+    }
+    std::vector<Tree> subtrees;
+    top: subtrees.emplace_back(ParseTree(begin, end));
+    switch (*begin++) {
+      case ',': goto top;
+      case ']': return Tree{std::move(subtrees)};
+      default: assert(false);
+    }
+  } else if (isdigit(*begin)) {
+    auto number_end = std::find_if_not(begin, end, isdigit);
+    std::string number_str {begin, number_end};
+    begin = number_end;
+    std::int64_t number = std::stoll(number_str);
+    return Tree{number};
+  } else {
+    assert(false);
+  }
+}
+
+auto Parse(std::istream & in) -> Input
+{
+  Input result;
+  std::string line;
+  while (std::getline(in, line)) {
+    auto cursor = line.begin();
+    result.push_back(ParseTree(cursor, line.end()));
+    std::getline(in, line);
+    cursor = line.begin();
+    result.push_back(ParseTree(cursor, line.end()));
+    std::getline(in, line); // skip blank
+  }
+
+  return result;
+}
+
+auto Part1(Input const& input) -> std::int64_t
+{
+  std::int64_t result {0};
+  for (std::size_t i = 0; i < input.size(); i += 2) {
+    if (input[i] < input[i+1]) {
+      result += i/2 + 1;
+    }
+  }
+  return result;
+}
+
+auto Part2(Input input) -> std::int64_t
+{
+  Tree two {std::vector{Tree{std::vector{Tree{2}}}}};
+  Tree six {std::vector{Tree{std::vector{Tree{6}}}}};
+  auto ix2 = std::count_if(input.begin(), input.end(), [&](auto x) { return x < two; });
+  auto ix6 = std::count_if(input.begin(), input.end(), [&](auto x) { return x < six; });
+  return (ix2+1) * (ix6+2);
+}
+
+} // namespace
+
+TEST_SUITE("2022-13 examples") {
+  TEST_CASE("simple ordering") {
+    CHECK(Tree{1} < Tree{2});
+    CHECK(!(Tree{2} < Tree{1}));
+    CHECK(Tree{std::vector{Tree{1}}} < Tree{std::vector{Tree{2}}});
+    CHECK(Tree{1} < Tree{std::vector{Tree{2}}});
+    CHECK(!(Tree{std::vector{Tree{2}}} < Tree{1}));
+    CHECK(Tree{std::vector<Tree>{}} < Tree{std::vector{Tree{2}}});
+    CHECK(Tree{std::vector<Tree>{}} < Tree{std::vector{Tree{2}}});
+  }
+  TEST_CASE("documented example") {
+    std::istringstream in {
+      "[1,1,3,1,1]\n"
+      "[1,1,5,1,1]\n"
+      "\n"
+      "[[1],[2,3,4]]\n"
+      "[[1],4]\n"
+      "\n"
+      "[9]\n"
+      "[[8,7,6]]\n"
+      "\n"
+      "[[4,4],4,4]\n"
+      "[[4,4],4,4,4]\n"
+      "\n"
+      "[7,7,7,7]\n"
+      "[7,7,7]\n"
+      "\n"
+      "[]\n"
+      "[3]\n"
+      "\n"
+      "[[[]]]\n"
+      "[[]]\n"
+      "\n"
+      "[1,[2,[3,[4,[5,6,7]]]],8,9]\n"
+      "[1,[2,[3,[4,[5,6,0]]]],8,9]\n"
+    };
+    auto input = Parse(in);
+    CHECK(13 == Part1(input));
+    CHECK(140 == Part2(input));
+  }
+}
+
+auto main(int argc, char** argv) -> int
+{
+  auto input = Parse(*aocpp::Startup(argc, argv));
+  std::cout << "count " << input.size() << std::endl;
+  std::cout << "Part 1: " << Part1(input) << std::endl;
+  std::cout << "Part 2: " << Part2(std::move(input)) << std::endl;
+}
diff --git a/2022/CMakeLists.txt b/2022/CMakeLists.txt
index 0857755..38f8acd 100644
--- a/2022/CMakeLists.txt
+++ b/2022/CMakeLists.txt
@@ -10,6 +10,9 @@ target_link_libraries(2022_04 aocpp)
 add_executable(2022_12 12.cpp)
 target_link_libraries(2022_12 aocpp)
 
+add_executable(2022_13 13.cpp)
+target_link_libraries(2022_13 aocpp)
+
 add_executable(2022_18 18.cpp)
 target_link_libraries(2022_18 aocpp)