From 5d5a44570c8b58e4034b742efe61aa3b8a9e98be Mon Sep 17 00:00:00 2001
From: Gnarwhal <git.aspect893@passmail.net>
Date: Thu, 17 Dec 2020 23:58:33 -0800
Subject: [PATCH] Completed day 18

---
 2020/days/day18.cpp | 128 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 128 insertions(+)
 create mode 100644 2020/days/day18.cpp

diff --git a/2020/days/day18.cpp b/2020/days/day18.cpp
new file mode 100644
index 0000000..c459a7a
--- /dev/null
+++ b/2020/days/day18.cpp
@@ -0,0 +1,128 @@
+/*******************************************************************************
+ *
+ * Copyright (c) 2020 Gnarwhal
+ *
+ * -----------------------------------------------------------------------------
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files(the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ *******************************************************************************/
+
+#include <vector>
+#include <string>
+#include <iostream>
+#include <fstream>
+
+#include "../misc/types.hpp"
+#include "../misc/print.hpp"
+
+auto evaluate_part1(const std::string & equation, usize & index) -> u64 {
+	auto value     = u64(0);
+	auto operation = 0;
+	while (equation[index] != ')') {
+		if ('0' <= equation[index] && equation[index] <= '9') {
+			auto end = index;
+			while ('0' <= equation[++end] && equation[end] <= '9');
+			if (operation == 0) {
+				value += std::stoll(equation.substr(index, end - index));
+			} else {
+				value *= std::stoll(equation.substr(index, end - index));
+			}
+			index = end;
+		} else if (equation[index] == '+') {
+			operation = 0;
+			index += 2;
+		} else if (equation[index] == '*') {
+			operation = 1;
+			index += 2;
+		} else if (equation[index] == '(') {
+			if (operation == 0) {
+				value += evaluate_part1(equation, ++index);
+			} else {
+				value *= evaluate_part1(equation, ++index);
+			}
+		} else if (equation[index] == ' ') {
+			++index;
+		}
+	}
+	++index;
+	return value;
+}
+
+auto evaluate_part2(const std::string & equation, usize & index) -> u64;
+auto evaluate_part2_addition(const std::string & equation, usize & index) -> u64;
+auto evaluate_part2_factor(const std::string & equation, usize & index) -> u64;
+
+auto evaluate_part2(const std::string & equation, usize & index) -> u64 {
+	auto value1 = evaluate_part2_addition(equation, index);
+	if (++index < equation.size() && equation[index] == '*') {
+		auto value2 = evaluate_part2(equation, index += 2);
+		return value1 * value2;
+	}
+	--index;
+	return value1;
+}
+
+auto evaluate_part2_addition(const std::string & equation, usize & index) -> u64 {
+	auto value1 = evaluate_part2_factor(equation, index);
+	if (++index < equation.size() && equation[index] == '+') {
+		auto value2 = evaluate_part2_addition(equation, index += 2);
+		return value1 + value2;
+	}
+	--index;
+	return value1;
+}
+
+auto evaluate_part2_factor(const std::string & equation, usize & index) -> u64 {
+	auto value = u64(0);
+	if (equation[index] == '(') {
+		value = evaluate_part2(equation, ++index);
+		++index;
+	} else {
+		auto end = index;
+		while ('0' <= equation[++end] && equation[end] <= '9');
+		value = std::stoll(equation.substr(index, end - index));
+		index = end;
+	}
+	return value;
+}
+
+auto day18() -> void {
+	auto equations = std::vector<std::string>();
+	{
+		auto line = std::string();
+		auto file = std::ifstream("inputs/day18.input");
+		while (getline(file, line)) {
+			equations.push_back(line + ')');
+		}
+	}
+	auto sum = u64(0);
+	for (auto i = usize(0); i < equations.size(); ++i) {
+		auto index = usize(0);
+		sum += evaluate_part1(equations[i], index);
+	}
+	print(sum);
+
+	sum = u64(0);
+	for (auto i = usize(0); i < equations.size(); ++i) {
+		auto index = usize(0);
+		sum += evaluate_part2_factor('(' + equations[i], index);
+	}
+	print(sum);
+}