From e8b5a045a8d7362b1ba8260a6987dd1b8ed282bf Mon Sep 17 00:00:00 2001
From: Eric Mertens <emertens@gmail.com>
Date: Sun, 20 Nov 2022 19:44:38 -0800
Subject: [PATCH] 2020/18

---
 2020/18.cpp         | 99 +++++++++++++++++++++++++++++++++++++++++++++
 2020/CMakeLists.txt |  3 ++
 2 files changed, 102 insertions(+)
 create mode 100644 2020/18.cpp

diff --git a/2020/18.cpp b/2020/18.cpp
new file mode 100644
index 0000000..d35564e
--- /dev/null
+++ b/2020/18.cpp
@@ -0,0 +1,99 @@
+#include <algorithm>
+#include <cctype>
+#include <cstdint>
+#include <cstdlib>
+#include <functional>
+#include <iostream>
+#include <map>
+#include <tuple>
+#include <vector>
+
+#include <doctest.h>
+
+#include <aocpp/Startup.hpp>
+
+namespace {
+
+auto Eval(
+  std::string const& input,
+  std::map<char, std::pair<int, std::function<std::int64_t(std::int64_t,std::int64_t)>>> cfg
+) -> std::int64_t
+{
+  std::vector<char> ops;
+  std::vector<std::int64_t> vals;
+  
+  auto const eval1 = [&](){
+    char o = ops.back(); ops.pop_back();
+    std::int64_t y = vals.back(); vals.pop_back();
+    std::int64_t x = vals.back(); vals.pop_back();
+    vals.push_back(cfg[o].second(x,y));
+  };
+
+  for (auto it = input.begin(); it != input.end(); it++) {
+    char const c = *it;
+    if (c == ' ') continue;
+    if (std::isdigit(c)) {
+      vals.push_back(c - '0');
+    } else if ('(' == c) {
+      ops.push_back('(');
+    } else if (')' == c) {
+      while (ops.back() != '(') eval1();
+      ops.pop_back();
+    } else if (auto opit = cfg.find(c); opit != cfg.end()) {
+      while (!ops.empty() && cfg[ops.back()].first >= opit->second.first) eval1();
+      ops.push_back(c);
+    }
+  }
+
+  while (!ops.empty()) eval1();
+
+  return vals.back();
+}
+
+auto Part1(std::string const& line) {
+  return Eval(line, {{'+', {1, std::plus<std::int64_t>()}},{'*', {1, std::multiplies<std::int64_t>()}}});
+}
+
+auto Part2(std::string const& line) {
+  return Eval(line, {{'+', {2, std::plus<std::int64_t>()}},{'*', {1, std::multiplies<std::int64_t>()}}});
+}
+
+} // namespace
+
+TEST_SUITE("documented examples") {
+
+TEST_CASE("part 1") {
+  REQUIRE(Part1("1 + 2 * 3 + 4 * 5 + 6") == 71);
+  REQUIRE(Part1("1 + (2 * 3) + (4 * (5 + 6))") == 51);
+  REQUIRE(Part1("2 * 3 + (4 * 5)") == 26);
+  REQUIRE(Part1("5 + (8 * 3 + 9 + 3 * 4 * 3)") == 437);
+  REQUIRE(Part1("5 * 9 * (7 * 3 * 3 + 9 * 3 + (8 + 6 * 4))") == 12240);
+  REQUIRE(Part1("((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2") == 13632);
+}
+
+TEST_CASE("part 2") {
+  REQUIRE(Part2("1 + 2 * 3 + 4 * 5 + 6") == 231);
+  REQUIRE(Part2("1 + (2 * 3) + (4 * (5 + 6))") == 51);
+  REQUIRE(Part2("2 * 3 + (4 * 5)") == 46);
+  REQUIRE(Part2("5 + (8 * 3 + 9 + 3 * 4 * 3)") == 1445);
+  REQUIRE(Part2("5 * 9 * (7 * 3 * 3 + 9 * 3 + (8 + 6 * 4))") == 669060);
+  REQUIRE(Part2("((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2") == 23340);
+}
+
+}
+
+auto main(int argc, char** argv) -> int {
+  auto & in = aocpp::Startup(argc, argv);
+
+  std::int64_t part1 = 0;
+  std::int64_t part2 = 0;
+  
+  std::string line;
+  while (std::getline(in, line)) {
+    part1 += Part1(line);
+    part2 += Part2(line);
+  }
+  
+  std::cout << "Part 1: " << part1 << std::endl;
+  std::cout << "Part 2: " << part2 << std::endl;
+}
diff --git a/2020/CMakeLists.txt b/2020/CMakeLists.txt
index 2a3ee47..6acd5ca 100644
--- a/2020/CMakeLists.txt
+++ b/2020/CMakeLists.txt
@@ -7,5 +7,8 @@ target_link_libraries(2020_03 aocpp)
 add_executable(2020_16 16.cpp)
 target_link_libraries(2020_16 aocpp dlx)
 
+add_executable(2020_18 18.cpp)
+target_link_libraries(2020_18 aocpp)
+
 add_executable(2020_21 21.cpp)
 target_link_libraries(2020_21 aocpp dlx)
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