From 277b24e9f4b17c164e71d27bc5d3c4373d8a8bcf Mon Sep 17 00:00:00 2001
From: Eric Mertens <emertens@galois.com>
Date: Tue, 24 Jan 2023 12:01:42 -0500
Subject: [PATCH] fiddle

---
 2022/06.cpp |  8 ++-----
 2022/09.cpp | 64 +++++++++++++++++++++++++++++++----------------------
 2022/20.cpp |  6 ++---
 3 files changed, 41 insertions(+), 37 deletions(-)

diff --git a/2022/06.cpp b/2022/06.cpp
index 60b5bdc..19b69fb 100644
--- a/2022/06.cpp
+++ b/2022/06.cpp
@@ -18,15 +18,11 @@ auto Solve(std::string const& input, std::size_t n) -> std::size_t
   std::size_t uniques {0};
 
   auto const inc = [&](char c) {
-    if (0 == counts[static_cast<std::uint8_t>(c)]++) {
-      uniques++;
-    }
+    uniques += 1 == ++counts[static_cast<std::uint8_t>(c)];
   };
 
   auto const dec = [&](char c) {
-    if (0 == --counts[static_cast<std::uint8_t>(c)]) {
-      uniques--;
-    }
+    uniques -= 0 == --counts[static_cast<std::uint8_t>(c)];
   };
 
   for (std::size_t i = 0; i < n; ++i) {
diff --git a/2022/09.cpp b/2022/09.cpp
index 7b84acf..ef438c9 100644
--- a/2022/09.cpp
+++ b/2022/09.cpp
@@ -15,9 +15,9 @@ using namespace aocpp;
 
 namespace {
 
-using Dir = Coord(*)(Coord);
+using DirFn = Coord(Coord);
 
-auto ToDir(char c) -> Dir {
+auto ToDir(char c) -> DirFn* {
   switch (c) {
     case 'L': return Left;
     case 'R': return Right;
@@ -35,38 +35,48 @@ auto Sign(std::int64_t x) -> std::int64_t
   return (x>0) - (x<0);
 }
 
-auto Solve(std::istream & in) -> std::pair<std::int64_t, std::int64_t>
-{
-  std::size_t constexpr knotn {10};
-  Coord knots[knotn] {};
-  std::set<Coord> p1{knots[1]}, p2{knots[9]};
-  char d;
-  long n;
+class Logic {
+  Coord knots[10] {}; // Current location of each knot in the rope
+  std::set<Coord> s1{{}}, s9{{}};
 
-  while (in >> d >> n) {
-    auto const dir = ToDir(d);
-    while (n--) {
-      knots[0] = dir(knots[0]);
-      
-      std::size_t k;
-      for (k = 1; k < knotn; ++k) {
-        auto const delta {knots[k-1] - knots[k]};
-        if (NormInf(delta) <= 1) {
-          break;
-        }
-        knots[k] += {Sign(delta.x), Sign(delta.y)};
+public:
+  auto answer() const -> std::pair<std::size_t, std::size_t>
+  {
+    return {s1.size(), s9.size()};
+  }
+
+  auto move(DirFn* dirFn) -> void
+  {
+    knots[0] = dirFn(knots[0]);
+    
+    std::size_t k;
+    for (k = 1; k < 10; ++k) {
+      auto const delta {knots[k-1] - knots[k]};
+      if (NormInf(delta) <= 1) {
+        break;
       }
+      knots[k] += {Sign(delta.x), Sign(delta.y)};
+    }
 
-      if (k > 1) {
-        p1.insert(knots[1]);
-        if (k > 9) {
-          p2.insert(knots[9]);
-        }
+    // only update the sets when a knot actually moved
+    if (k > 1) {
+      s1.insert(knots[1]);
+      if (k > 9) {
+        s9.insert(knots[9]);
       }
     }
   }
+};
 
-  return {p1.size(), p2.size()};
+auto Solve(std::istream & in) -> std::pair<std::size_t, std::size_t>
+{
+  Logic logic;
+  char d;
+  std::size_t n;
+  while (in >> d >> n) {
+    while (n--) { logic.move(ToDir(d)); }
+  }
+  return logic.answer();
 }
 
 } // namespace
diff --git a/2022/20.cpp b/2022/20.cpp
index a40c0fa..879d1e7 100644
--- a/2022/20.cpp
+++ b/2022/20.cpp
@@ -33,10 +33,8 @@ auto Solve(Input const& input, std::size_t const rounds) -> std::int64_t
   std::size_t const len = input.size();
   std::vector<std::size_t> fwds(len), bwds(len);
 
-  for (std::size_t i = 0; i < len; ++i) {
-    fwds[i] = aocpp::Mod<std::int64_t>(i+1, len);
-    bwds[i] = aocpp::Mod<std::int64_t>(i-1, len);
-  }
+  std::iota(fwds.begin(), fwds.end()-1, 1); fwds.back() = 0;
+  std::iota(bwds.begin()+1, bwds.end(), 0); bwds.front() = len-1; 
 
   for (std::size_t r = 0; r < rounds; ++r) {
     for (std::size_t i = 0; i < len; ++i) {