From 56e890cec0a28c0a485212ccebfaf774235a79a2 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Wed, 3 Jan 2024 23:35:54 +0100
Subject: prepare for more puzzles ... :)

---
 2023/src/day04.cpp | 114 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 114 insertions(+)
 create mode 100644 2023/src/day04.cpp

(limited to '2023/src/day04.cpp')

diff --git a/2023/src/day04.cpp b/2023/src/day04.cpp
new file mode 100644
index 0000000..0d3e552
--- /dev/null
+++ b/2023/src/day04.cpp
@@ -0,0 +1,114 @@
+#include <fstream>
+#include <iostream>
+#include <set>
+#include <sstream>
+#include <string>
+#include <string_view>
+#include <vector>
+
+using namespace std;
+
+vector<string>
+read_file(string_view filename)
+{
+	fstream        input{ filename };
+	vector<string> data;
+
+	for ( string line; getline(input, line); ) {
+		data.emplace_back(line);
+	}
+
+	return data;
+}
+
+vector<string>
+split(const string& line, char sep)
+{
+	stringstream   input{ line };
+	vector<string> parts;
+
+	for ( string part; getline(input, part, sep); ) {
+		parts.emplace_back(part);
+	}
+
+	return parts;
+}
+
+template<typename Container>
+Container
+read_ints(const string& line)
+{
+	Container    container{};
+	stringstream input{ line };
+
+	for ( typename Container::value_type value; input >> value; ) {
+		container.emplace(value);
+	}
+
+	return container;
+}
+
+auto
+build_data_set(string_view filename)
+{
+	vector<unsigned long> values;
+
+	for ( const auto& line: read_file(filename) ) {
+		const auto cards   = split(line, ':');
+		const auto numbers = split(cards[1], '|');
+
+		const auto winning_numbers = read_ints<set<int>>(numbers[0]);
+		const auto card_numbers    = read_ints<set<int>>(numbers[1]);
+
+		auto count = 0U;
+		for ( auto number: winning_numbers ) {
+			if ( card_numbers.contains(number) ) {
+				++count;
+			}
+		}
+		values.emplace_back(count);
+	}
+
+	return values;
+}
+
+void
+pass1(const vector<unsigned long>& values)
+{
+	auto sum = 0U;
+	for ( auto value: values ) {
+		if ( value != 0 ) {
+			sum += (1U << (value - 1));
+		}
+	}
+
+	cout << sum << endl;
+}
+
+void
+pass2(const vector<unsigned long>& values)
+{
+	auto count = 0U;
+
+	function<void(size_t, size_t)> process = [&](size_t start, size_t end) -> void {
+		for ( ; start != end; ++start ) {
+			auto value = values[start];
+
+			++count;
+
+			process(start + 1, start + value + 1);
+		}
+	};
+
+	process(0, values.size());
+
+	cout << count << endl;
+}
+
+int
+main()
+{
+	const auto values = build_data_set("data/day04.txt");
+	pass1(values);
+	pass2(values);
+}
-- 
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