From f52b43d879218febd8d2cb69d74d94af8ec1fe31 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Fri, 13 Dec 2024 12:41:13 +0100
Subject: aoc 2024, day 13

---
 2024/src/day13.cpp | 120 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 120 insertions(+)
 create mode 100644 2024/src/day13.cpp

diff --git a/2024/src/day13.cpp b/2024/src/day13.cpp
new file mode 100644
index 0000000..9ba58ba
--- /dev/null
+++ b/2024/src/day13.cpp
@@ -0,0 +1,120 @@
+#include <array>
+#include <fstream>
+#include <iostream>
+#include <iterator>
+#include <numeric>
+#include <regex>
+#include <vector>
+using namespace std;
+
+vector<string>
+split(string_view line, string_view delimiter)
+{
+	string::size_type pos_start = 0;
+	string::size_type pos_end   = 0;
+
+	vector<string> res;
+	while ( (pos_end = line.find(delimiter, pos_start)) != string::npos ) {
+		res.emplace_back(line.substr(pos_start, pos_end - pos_start));
+
+		pos_start = pos_end + delimiter.length();
+	}
+	if ( pos_start != line.size() ) {
+		res.emplace_back(line.substr(pos_start));
+	}
+	return res;
+}
+
+vector<array<long, 6>>
+read_file(string_view filename)
+{
+	static const regex pattern{ R"((\d+).*\+(\d+).*\+(\d+).*\+(\d+).*=(\d+).*=(\d+))" };
+
+	fstream input{ filename };
+	string  content{ istreambuf_iterator<char>{ input }, {} };
+
+	auto parts = split(content, "\n\n");
+
+	vector<array<long, 6>> data;
+	for ( auto part: parts ) {
+		part.erase(std::remove(part.begin(), part.end(), '\n'), part.cend());
+
+		smatch matches;
+		if ( regex_search(part, matches, pattern) ) {
+			data.push_back({ stoi(matches[1]),
+			                 stoi(matches[2]),
+			                 stoi(matches[3]),
+			                 stoi(matches[4]),
+			                 stoi(matches[5]),
+			                 stoi(matches[6]) });
+		}
+	}
+
+	return data;
+}
+
+long
+test_brute_force(const array<long, 6>& machine)
+{
+	const auto button_a_x = machine[0];
+	const auto button_a_y = machine[1];
+	const auto button_b_x = machine[2];
+	const auto button_b_y = machine[3];
+	const auto price_x    = machine[4];
+	const auto price_y    = machine[5];
+
+	auto min_value = numeric_limits<long>::max();
+	for ( long i = 0; i != 100; ++i ) {
+		for ( long j = 0; j != 100; ++j ) {
+			if ( i * button_a_x + j * button_b_x == price_x &&
+			     i * button_a_y + j * button_b_y == price_y ) {
+				min_value = min(min_value, i * 3 + j);
+			}
+		}
+	}
+	return min_value != numeric_limits<long>::max() ? min_value : 0;
+}
+
+long
+test_algorithmic(const array<long, 6>& machine)
+{
+	const auto button_a_x = machine[0];
+	const auto button_a_y = machine[1];
+	const auto button_b_x = machine[2];
+	const auto button_b_y = machine[3];
+	const auto price_x    = machine[4] + 10000000000000;
+	const auto price_y    = machine[5] + 10000000000000;
+
+	const auto i = (price_x * button_b_y - price_y * button_b_x) / (button_a_x * button_b_y - button_a_y * button_b_x);
+	const auto j = (price_x - button_a_x * i) / button_b_x;
+
+	if ( i * button_a_x + j * button_b_x == price_x &&
+	     i * button_a_y + j * button_b_y == price_y ) {
+		return i * 3 + j;
+	}
+	return 0;
+}
+
+void
+part1(const vector<array<long, 6>>& machines)
+{
+	cout << accumulate(machines.begin(), machines.end(), 0L, [](auto init, const auto& machine) {
+		return init + test_brute_force(machine);
+	}) << endl;
+}
+
+void
+part2(const vector<array<long, 6>>& machines)
+{
+	cout << accumulate(machines.begin(), machines.end(), 0L, [](auto init, const auto& machine) {
+		return init + test_algorithmic(machine);
+	}) << endl;
+}
+
+int
+main()
+{
+	auto data = read_file("data/day13.txt");
+	part1(data);
+	part2(data);
+}
-- 
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