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 ... :)

---
 2020/src/day01.cpp | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 2020/src/day01.cpp

(limited to '2020/src/day01.cpp')

diff --git a/2020/src/day01.cpp b/2020/src/day01.cpp
new file mode 100644
index 0000000..d2d8629
--- /dev/null
+++ b/2020/src/day01.cpp
@@ -0,0 +1,55 @@
+#include <fstream>
+#include <functional>
+#include <iostream>
+#include <string>
+#include <vector>
+#include <numeric>
+using namespace std;
+
+auto
+read_file(string_view filename)
+{
+	fstream      input{ filename };
+	vector<long> data;
+
+	for ( long value = 0; input >> value; ) {
+		data.emplace_back(value);
+	}
+
+	return data;
+}
+
+void
+process(const vector<long>& values)
+{
+	const long year = 2020;
+
+	if (accumulate(values.begin(), values.end(), 0L) == year) {
+		cout << accumulate(values.begin(), values.end(), 1, multiplies<>()) << endl;
+	}
+}
+
+void
+combination(const vector<long>& values, size_t r)
+{
+	vector<bool> v(values.size());
+	fill(v.end() - long(r), v.end(), true);
+	vector<long> set(r);
+	do {
+		set.clear();
+		for ( size_t i = 0; i != values.size(); ++i ) {
+			if ( v[i] ) {
+				set.emplace_back(values[i]);
+			}
+		}
+		process(set);
+	} while ( std::next_permutation(v.begin(), v.end()) );
+}
+
+int
+main()
+{
+	auto values = read_file("data/day01-sample1.txt");
+	combination(values, 2);
+	combination(values, 3);
+}
-- 
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