From 3d25bbb7e6cc67dc96e6c1f40ae901bd2bb754da Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Thu, 5 Dec 2024 22:32:08 +0100
Subject: aoc 2024, day5

---
 2024/src/day05.cpp | 104 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 104 insertions(+)
 create mode 100644 2024/src/day05.cpp

(limited to '2024/src/day05.cpp')

diff --git a/2024/src/day05.cpp b/2024/src/day05.cpp
new file mode 100644
index 0000000..37d74c6
--- /dev/null
+++ b/2024/src/day05.cpp
@@ -0,0 +1,104 @@
+#include <fstream>
+#include <iostream>
+#include <numeric>
+#include <set>
+#include <sstream>
+#include <string>
+#include <vector>
+using namespace std;
+
+vector<long>
+split(const string& line, char sep = ',')
+{
+	vector<long> parts;
+	stringstream input{ line };
+
+	for ( string part; getline(input, part, sep); ) {
+		parts.emplace_back(stol(part));
+	}
+
+	return parts;
+}
+
+tuple<vector<tuple<long, long>>, vector<vector<long>>>
+read_file(string_view filename)
+{
+	fstream input{ filename };
+
+	vector<tuple<long, long>> rules;
+	for ( string line; getline(input, line); ) {
+		if ( line.empty() ) {
+			break;
+		}
+		long lhs = 0;
+		long rhs = 0;
+		sscanf(line.c_str(), "%ld|%ld", &lhs, &rhs); // NOLINT
+		rules.emplace_back(lhs, rhs);
+	}
+
+	vector<vector<long>> pages;
+	for ( string line; getline(input, line); ) {
+		pages.emplace_back(split(line));
+	}
+	return { rules, pages };
+}
+
+bool
+is_valid(const vector<tuple<long, long>>& rules, const vector<long>& page)
+{
+	set<long> processed;
+
+	bool invalid = false;
+	for ( const auto& num: page ) {
+		processed.emplace(num);
+
+		auto pred = [num](const tuple<long, long>& rule) {
+			return get<0>(rule) == num;
+		};
+
+		for ( auto it = find_if(rules.begin(), rules.end(), pred); it != rules.end(); it = find_if(it + 1, rules.end(), pred) ) {
+			const auto foo = get<1>(*it);
+
+			if ( processed.contains(foo) ) {
+				invalid = true;
+			}
+		}
+	}
+	return !invalid;
+}
+
+void
+part1(const vector<tuple<long, long>>& rules, const vector<vector<long>>& pages)
+{
+	long sum = 0;
+	for ( const auto& page: pages ) {
+		if ( is_valid(rules, page) ) {
+			sum += page.at(page.size() / 2);
+		}
+	}
+	cout << sum << endl;
+}
+
+void
+part2(const vector<tuple<long, long>>& rules, const vector<vector<long>>& pages)
+{
+	long sum = 0;
+	for ( auto page: pages ) {
+		if ( !is_valid(rules, page) ) {
+			ranges::sort(page, [&](auto lhs, auto rhs) -> bool {
+				return ranges::find(rules, make_tuple(lhs, rhs)) != rules.end();
+			});
+
+			sum += page.at(page.size() / 2);
+		}
+	}
+	cout << sum << endl;
+}
+
+int
+main()
+{
+	auto [rules, pages] = read_file("data/day05.txt");
+	part1(rules, pages);
+	part2(rules, pages);
+}
-- 
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