From ab1af5a087d4dba1b928cb2e430457661c4be3d2 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Wed, 20 Nov 2024 22:46:18 +0100
Subject: aoc 2015, day 21

---
 2015/src/day21.cpp | 181 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 181 insertions(+)
 create mode 100644 2015/src/day21.cpp

diff --git a/2015/src/day21.cpp b/2015/src/day21.cpp
new file mode 100644
index 0000000..2a38c86
--- /dev/null
+++ b/2015/src/day21.cpp
@@ -0,0 +1,181 @@
+#include <array>
+#include <fstream>
+#include <iostream>
+#include <sstream>
+using namespace std;
+
+struct Item {
+	Item(string_view name, int cost, int damage, int armor)
+	    : name_(name)
+	    , cost_(cost)
+	    , damage_(damage)
+	    , armor_(armor)
+	{
+	}
+
+	const string name_;
+	const int    cost_;
+	const int    damage_;
+	const int    armor_;
+};
+
+struct Boss {
+	int hit_points_;
+	int damage_;
+	int armor_;
+};
+
+struct Player {
+	Player(const Item& weapon, const Item& armor, const tuple<Item, Item>& rings)
+	    : damage_(weapon.damage_ + armor.damage_ + get<0>(rings).damage_ + get<1>(rings).damage_)
+	    , armor_(weapon.armor_ + armor.armor_ + get<0>(rings).armor_ + get<1>(rings).armor_)
+	{
+	}
+
+	int hit_points_{ 100 };
+	int damage_;
+	int armor_;
+
+	bool would_win_against(Boss boss)
+	{
+		while ( true ) {
+			auto player_damage = max(1, damage_ - boss.armor_);
+			boss.hit_points_ -= player_damage;
+			if ( boss.hit_points_ <= 0 ) {
+				return true;
+			}
+
+			auto boss_damage = max(1, boss.damage_ - armor_);
+			hit_points_ -= boss_damage;
+			if ( hit_points_ <= 0 ) {
+				return false;
+			}
+		}
+	}
+};
+
+const array<Item, 5> weapons = {
+	Item("Dagger", 8, 4, 0),
+	Item("Shortsword", 10, 5, 0),
+	Item("Warhammer", 25, 6, 0),
+	Item("Longsword", 40, 7, 0),
+	Item("Greataxe", 74, 8, 0)
+};
+
+const array<Item, 6> armors = {
+	Item("Leather", 13, 0, 1),
+	Item("Chainmail", 31, 0, 2),
+	Item("Splintmail", 53, 0, 3),
+	Item("Bandedmail", 75, 0, 4),
+	Item("Platemail", 102, 0, 5),
+	Item("Noting", 0, 0, 0)
+};
+
+vector<tuple<Item, Item>>
+generate_ring_pairs()
+{
+	const array<Item, 7> rings = {
+		Item("Damage +1", 25, 1, 0),
+		Item("Damage +2", 50, 2, 0),
+		Item("Damage +3", 100, 3, 0),
+		Item("Defense +1", 20, 0, 1),
+		Item("Defense +2", 40, 0, 2),
+		Item("Defense +3", 80, 0, 3),
+		Item("Nothing 0", 0, 0, 0)
+	};
+
+	vector<tuple<Item, Item>> pairs;
+
+	for ( size_t i = 0; i < rings.size(); ++i ) {
+		for ( size_t j = i + 1; j < rings.size(); ++j ) {
+			pairs.emplace_back(rings.at(i), rings.at(j));
+		}
+	}
+
+	pairs.emplace_back(rings.back(), rings.back());
+
+	return pairs;
+}
+
+auto
+split(const string& line, char sep = ' ')
+{
+	vector<string> parts;
+	stringstream   input{ line };
+
+	for ( string part; getline(input, part, sep); ) {
+		parts.emplace_back(part);
+	}
+
+	return parts;
+}
+
+Boss
+read_file(string_view filename)
+{
+	fstream input{ filename };
+	Boss    boss{};
+
+	for ( string line; getline(input, line); ) {
+		auto parts = split(line);
+
+		if ( parts[0] == "Hit" ) {
+			boss.hit_points_ = stoi(parts[2]);
+		}
+		else if ( parts[0] == "Damage:" ) {
+			boss.damage_ = stoi(parts[1]);
+		}
+		else if ( parts[0] == "Armor:" ) {
+			boss.armor_ = stoi(parts[1]);
+		}
+	}
+	return boss;
+}
+
+void
+part1(const Boss& boss)
+{
+	auto rings = generate_ring_pairs();
+
+	auto min_cost = numeric_limits<int>::max();
+	for ( const auto& weapon: weapons ) {
+		for ( const auto& armor: armors ) {
+			for ( const auto& ring_pair: rings ) {
+				Player player(weapon, armor, ring_pair);
+
+				if (player.would_win_against(boss)) {
+					min_cost = min(min_cost, weapon.cost_ + armor.cost_ + get<0>(ring_pair).cost_ + get<1>(ring_pair).cost_);
+				}
+			}
+		}
+	}
+	cout << min_cost << endl;
+}
+
+void
+part2(const Boss& boss)
+{
+	auto rings = generate_ring_pairs();
+
+	auto max_cost = numeric_limits<int>::min();
+	for ( const auto& weapon: weapons ) {
+		for ( const auto& armor: armors ) {
+			for ( const auto& ring_pair: rings ) {
+				Player player(weapon, armor, ring_pair);
+
+				if (!player.would_win_against(boss)) {
+					max_cost = max(max_cost, weapon.cost_ + armor.cost_ + get<0>(ring_pair).cost_ + get<1>(ring_pair).cost_);
+				}
+			}
+		}
+	}
+	cout << max_cost << endl;
+}
+
+int
+main()
+{
+	auto boss = read_file("data/day21.txt");
+	part1(boss);
+	part2(boss);
+}
-- 
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