From d5cd72f4bc9fa29d917af652a4bbb04cf0422ddb Mon Sep 17 00:00:00 2001
From: Eric Mertens <emertens@galois.com>
Date: Mon, 27 Mar 2023 15:59:12 -0700
Subject: [PATCH] make 13 more efficient! (no more temporaries)

---
 2022/13.cpp | 65 ++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 42 insertions(+), 23 deletions(-)

diff --git a/2022/13.cpp b/2022/13.cpp
index 3cc4d5f..ea6b720 100644
--- a/2022/13.cpp
+++ b/2022/13.cpp
@@ -9,29 +9,49 @@
 #include <doctest.h>
 
 #include <aocpp/Startup.hpp>
+#include <aocpp/Overloaded.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);
-      }
-    }
-  }
+  std::variant<std::int64_t, std::vector<Tree>> rep;
 };
 
+auto operator<(Tree const& lhs, Tree const& rhs) -> bool;
+
+auto operator<(std::vector<Tree> const& x, std::int64_t y) -> bool;
+auto operator<(std::int64_t x, std::vector<Tree> const& y) -> bool;
+
+auto operator<(Tree const& x, std::int64_t y) -> bool;
+auto operator<(std::int64_t x, Tree const& y) -> bool;
+
+auto operator<(std::int64_t x, std::vector<Tree> const& y) -> bool {
+  switch (y.size()) {
+    case 0: return false;
+    case 1: return x < y[0];
+    default: return !(y[0] < x);
+  }
+}
+
+auto operator<(std::vector<Tree> const& x, std::int64_t y) -> bool {
+  switch (x.size()) {
+    case 0: return true;
+    default: return x[0] < y;
+  }
+}
+
+auto operator<(Tree const& x, std::int64_t y) -> bool {
+  return std::visit([y](auto const& x_) { return x_ < y; }, x.rep);
+}
+
+auto operator<(std::int64_t x, Tree const& y) -> bool {
+  return std::visit([x](auto const& y_) { return x < y_; }, y.rep);
+}
+
+auto operator<(Tree const& lhs, Tree const& rhs) -> bool {
+  return std::visit(std::less(), lhs.rep, rhs.rep);
+}
+
 using Input = std::vector<Tree>;
 
 auto ParseTree(std::string::iterator & begin, std::string::iterator end) -> Tree
@@ -87,12 +107,12 @@ auto Part1(Input const& input) -> std::int64_t
   return result;
 }
 
-auto Part2(Input input) -> std::int64_t
+auto Part2(Input const& 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; });
+  auto ix2 = std::count_if(input.begin(), input.end(), [&](auto const& x) { return x < two; });
+  auto ix6 = std::count_if(input.begin(), input.end(), [&](auto const& x) { return x < six; });
   return (ix2+1) * (ix6+2);
 }
 
@@ -142,8 +162,7 @@ TEST_SUITE("2022-13 examples") {
 
 auto Main(std::istream & in, std::ostream & out) -> void
 {
-  auto input = Parse(in);
-  out << "count " << input.size() << std::endl;
+  auto const input = Parse(in);
   out << "Part 1: " << Part1(input) << std::endl;
-  out << "Part 2: " << Part2(std::move(input)) << std::endl;
+  out << "Part 2: " << Part2(input) << std::endl;
 }