diff --git a/2022/13.cpp b/2022/13.cpp
index eb3a04f..9386918 100644
--- a/2022/13.cpp
+++ b/2022/13.cpp
@@ -2,6 +2,7 @@
 #include <cstdint>
 #include <iostream>
 #include <sstream>
+#include <stdexcept>
 #include <variant>
 #include <vector>
 
diff --git a/2022/14.cpp b/2022/14.cpp
index def2cc7..c0e4d90 100644
--- a/2022/14.cpp
+++ b/2022/14.cpp
@@ -4,6 +4,7 @@
 #include <iostream>
 #include <sstream>
 #include <stack>
+#include <stdexcept>
 #include <tuple>
 #include <unordered_set>
 #include <vector>
diff --git a/2022/16.cpp b/2022/16.cpp
index 06f4ef5..fb80757 100644
--- a/2022/16.cpp
+++ b/2022/16.cpp
@@ -12,6 +12,7 @@
 #include <cstdint>
 #include <iostream>
 #include <sstream>
+#include <stack>
 #include <stdexcept>
 #include <string>
 #include <tuple>
@@ -90,8 +91,8 @@ struct Room {
 /// * Valve **name** has flow rate= **number** ; tunnel leads to valve **name**
 auto Parse(std::istream & in) -> std::vector<Room>
 {
-  std::vector<Room> result;
-  std::string line;
+  auto result = std::vector<Room>{};
+  auto line = std::string{};
   while (std::getline(in, line)) {
     using namespace qi::labels;
     using It = std::string::const_iterator;
@@ -108,8 +109,8 @@ auto Parse(std::istream & in) -> std::vector<Room>
       " " >>
       (name % ", ") [ phx::bind(&Room::connections, _val) = _1 ];
 
-    It b = line.begin();
-    It const e = line.end();
+    auto b = line.cbegin();
+    auto const e = line.cend();
     result.emplace_back();
     if (!qi::parse(b, e, room_description, result.back()) || b != e) {
       throw std::runtime_error{"bad input line"};
@@ -138,15 +139,15 @@ auto GenerateDistances(
   std::vector<Room> const& rooms
 ) -> std::pair<std::size_t, distance_array<std::uint64_t>>
 {
-  auto const N {rooms.size()};
+  auto const N = rooms.size();
 
   // Associate the names and indexes of each room
   std::unordered_map<std::string, std::size_t> names;
-  for (auto [i,room] : rooms | boost::adaptors::indexed()) {
+  for (auto const [i,room] : boost::adaptors::index(rooms)) {
     names[room.name] = i;
   }
 
-  distance_array<std::uint64_t> distances{boost::extents[N][N]};
+  auto distances = distance_array<std::uint64_t>{boost::extents[N][N]};
 
   for (auto const i : boost::irange(rooms.size())) {
     auto di = distances[i];
@@ -201,13 +202,15 @@ auto Routes(
   }
 
   // Maximal flow seen at each set of open valves
-  std::unordered_map<Valves, std::uint64_t> result;
+  auto result = std::unordered_map<Valves, std::uint64_t>{};
 
   // Remaining states for depth first search
-  std::vector<State> states {{initial_time, 0, start, {}}};
+  auto states = std::stack<State>{};
+  states.push({initial_time, 0, start, {}});
+
   while (!states.empty()) {
-    auto const state = states.back();
-    states.pop_back();
+    auto const state = states.top();
+    states.pop();
 
     if (auto & best = result[state.valves]; best < state.flow) {
       best = state.flow;
@@ -215,7 +218,7 @@ auto Routes(
 
     auto const distances_i = distances[state.location];
 
-    for (auto const [j, room] : rooms | boost::adaptors::indexed()) {
+    for (auto const [j, room] : boost::adaptors::index(rooms)) {
       // don't revisit a valve
       if (state.valves.test(j)) { continue; }
 
@@ -229,7 +232,7 @@ auto Routes(
       auto valves = state.valves;
       valves.set(j);
 
-      states.push_back({time, flow, static_cast<std::size_t>(j), valves});
+      states.push({time, flow, static_cast<std::size_t>(j), valves});
     }
   }
 
@@ -265,7 +268,7 @@ auto Part2(
   auto const routes = Routes(start, 26, rooms, distances);
   auto const end = routes.end();
 
-  std::uint64_t best {0};
+  auto best = std::uint64_t{0};
   for (auto it1 = routes.begin(); it1 != end; ++it1) {
     for (auto it2 = std::next(it1); it2 != end; ++it2) {
       // only consider pairs that have disjoint sets of valves
@@ -285,7 +288,7 @@ auto Part2(
 auto Main(std::istream & in, std::ostream & out) -> void
 {
   auto rooms = Parse(in);
-  auto const n = FlowsFirst(rooms);
+  auto const n = FlowsFirst(rooms); // reorders rooms
   auto const [start, distances] = GenerateDistances(rooms);
   rooms.resize(n); // forget about the rooms with no flow
   out << "Part 1: " << Part1(start, rooms, distances) << std::endl;
@@ -306,13 +309,13 @@ Valve HH has flow rate=22; tunnel leads to valve GG
 Valve II has flow rate=0; tunnels lead to valves AA, JJ
 Valve JJ has flow rate=21; tunnel leads to valve II
 )"};
-    std::ostringstream out;
+    auto out = std::ostringstream{};
     Main(in, out);
     CHECK(out.str() == "Part 1: 1651\nPart 2: 1707\n");
   }
 
   TEST_CASE("shortest path") {
-    distance_array<int> distances{boost::extents[4][4]};
+    auto distances = distance_array<int>{boost::extents[4][4]};
     std::fill_n(distances.data(), distances.num_elements(), 100);
 
     distances[0][2] = -2;
diff --git a/2022/18.cpp b/2022/18.cpp
index 9a98b0e..2713944 100644
--- a/2022/18.cpp
+++ b/2022/18.cpp
@@ -4,6 +4,7 @@
 #include <iostream>
 #include <set>
 #include <sstream>
+#include <stack>
 #include <stdexcept>
 #include <string>
 #include <tuple>
@@ -24,12 +25,14 @@ using Coord = aocpp::Vec<std::int64_t, 3>;
 /// @return set of coordinates
 auto Parse(std::istream & in) -> std::set<Coord>
 {
-  std::set<Coord> result;
-  std::string line;
+  auto result = std::set<Coord>{};
+  auto line = std::string{};
+
   while (in >> line) {
-    Coord x;
-    if (3 != std::sscanf(line.c_str(), "%lld,%lld,%lld\n", &x[0], &x[1], &x[2]))
+    auto x = Coord{};
+    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;
@@ -37,8 +40,8 @@ auto Parse(std::istream & in) -> std::set<Coord>
 
 auto Part1(std::set<Coord> const& obj) -> std::size_t
 {
-  std::size_t result {0};
-  for (auto && x : obj) {
+  auto result = std::size_t{0};
+  for (auto const& x : obj) {
     x.EachNeighbor([&](Coord const& y) {
       if (!obj.contains(y)) result++;
     });
@@ -49,21 +52,24 @@ auto Part1(std::set<Coord> const& obj) -> std::size_t
 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);
+  lo -= Coord{1};
+  hi += Coord{1};
 
-  std::set<Coord> seen {lo};
-  std::vector<Coord> work {lo};
-  std::size_t result {0};
+  auto seen = std::set<Coord>{};
+  auto work = std::stack<Coord>{};
+  auto result = std::size_t{0};
+  
+  work.push(lo);
+  seen.insert(lo);
 
   while (!work.empty()) {
-    auto x = work.back();
-    work.pop_back();
+    auto const x = work.top();
+    work.pop();
     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);
+        work.push(y);
       }
     });
   }
@@ -98,7 +104,7 @@ TEST_SUITE("2022-12 examples") {
 
 auto Main(std::istream & in, std::ostream & out) -> void
 {
-  auto const obj {Parse(in)};
+  auto const obj = Parse(in);
   out << "Part 1: " << Part1(obj) << std::endl;
   out << "Part 2: " << Part2(obj) << std::endl;
 }
diff --git a/2022/20.cpp b/2022/20.cpp
index 226473a..b56b3c9 100644
--- a/2022/20.cpp
+++ b/2022/20.cpp
@@ -4,6 +4,7 @@
 #include <iterator>
 #include <numeric>
 #include <sstream>
+#include <stdexcept>
 #include <string>
 #include <tuple>
 #include <vector>
@@ -24,7 +25,7 @@ using Input = std::vector<std::int64_t>;
 /// @return outer list of elves, inner lists of calories
 auto Parse(std::istream & in) -> Input
 {
-  Input result;
+  auto result = Input{};
   using It = std::istream_iterator<std::int64_t>;
   std::copy<It>(in, {}, std::back_inserter(result));
   return result;
@@ -33,7 +34,17 @@ auto Parse(std::istream & in) -> Input
 auto Solve(Input const& input, std::size_t const rounds) -> std::int64_t
 {
   auto const len = input.size();
-  std::vector<std::size_t> fwds(len), bwds(len);
+  auto fwds = std::vector<std::size_t>(len);
+  auto bwds = std::vector<std::size_t>(len);
+
+  if (len == 0) {
+    throw std::runtime_error{"Input too small"};
+  }
+
+  auto const zero_it = std::find(input.begin(), input.end(), 0);
+  if (zero_it == input.end()) {
+    throw std::runtime_error{"no zero element in input"};
+  }
 
   std::iota(fwds.begin(), fwds.end()-1, 1); fwds.back() = 0;
   std::iota(bwds.begin()+1, bwds.end(), 0); bwds.front() = len-1; 
@@ -67,8 +78,8 @@ auto Solve(Input const& input, std::size_t const rounds) -> std::int64_t
     }
   }
 
-  std::int64_t sum {0};
-  auto cursor = std::distance(input.begin(), std::find(input.begin(), input.end(), 0));
+  auto sum = std::int64_t{0};
+  auto cursor = std::distance(input.begin(), zero_it);
   for (auto const _ : boost::irange(3)) {
     for (auto const _ : boost::irange(1000)) {
       cursor = fwds[cursor];
@@ -86,7 +97,7 @@ auto Part1(Input const& input) -> std::int64_t
 
 auto Part2(Input input) -> std::int64_t
 {
-  for (auto& x : input) { x *= 811589153; }
+  for (auto& x : input) { x *= 811'589'153; }
   return Solve(input, 10);
 }
 
@@ -104,13 +115,13 @@ TEST_SUITE("2022-20 examples") {
       "4\n"};
       auto input = Parse(in);
       CHECK(3 == Part1(input));
-      CHECK(1623178306 == Part2(input));
+      CHECK(1623178306 == Part2(std::move(input)));
   }
 }
 
 auto Main(std::istream & in, std::ostream & out) -> void
 {
-  auto input {Parse(in)};
+  auto input = Parse(in);
   out << "Part 1: " << Part1(input) << std::endl;
   out << "Part 2: " << Part2(std::move(input)) << std::endl;
 }
diff --git a/2022/21.cpp b/2022/21.cpp
index 1c700e2..babe1e2 100644
--- a/2022/21.cpp
+++ b/2022/21.cpp
@@ -1,6 +1,7 @@
 #include <cstdint>
 #include <iostream>
 #include <sstream>
+#include <stdexcept>
 #include <string>
 #include <unordered_map>
 #include <variant>