From ec402bc00c7ab5774e355e56b141c2f6ff1340d5 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Sat, 9 Dec 2023 10:37:27 +0100
Subject: Lösung für Tag 9
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 src/day09.cpp | 107 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)
 create mode 100644 src/day09.cpp

(limited to 'src')

diff --git a/src/day09.cpp b/src/day09.cpp
new file mode 100644
index 0000000..1afcfe2
--- /dev/null
+++ b/src/day09.cpp
@@ -0,0 +1,107 @@
+#include <fstream>
+#include <iostream>
+#include <sstream>
+#include <string>
+#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;
+}
+
+template<typename T = long>
+vector<T>
+read_ints(const string& line)
+{
+	stringstream iss{ line };
+	return vector<T>{ istream_iterator<T>{ iss }, istream_iterator<T>{} };
+}
+
+template<typename T>
+void
+solve_rec_part1(vector<T>& values)
+{
+	vector<T> differences;
+
+	for ( size_t idx = 1; idx < values.size(); ++idx ) {
+		auto difference = values[idx] - values[idx - 1];
+		differences.emplace_back(difference);
+	}
+	auto all_zeros = all_of(differences.begin(), differences.end(), [](long diff) { return diff == 0; });
+	if ( !all_zeros) {
+		solve_rec_part1(differences);
+	}
+	else {
+		differences.emplace_back(0);
+	}
+	auto last_value = values.back();
+	auto last_difference = differences.back();
+	values.emplace_back(last_value + last_difference);
+}
+
+void
+part1()
+{
+	auto lines = read_file("data/day09.txt");
+
+	long sum = 0;
+	for ( const auto& line: lines ) {
+		auto values = read_ints(line);
+		solve_rec_part1(values);
+		sum += values.back();
+	}
+	cout << sum << endl;
+}
+
+template<typename T>
+void
+solve_rec_part2(vector<T>& values)
+{
+	vector<T> differences;
+
+	for ( size_t idx = 1; idx < values.size(); ++idx ) {
+		auto difference = values[idx] - values[idx - 1];
+		differences.emplace_back(difference);
+	}
+	auto all_zeros = all_of(differences.begin(), differences.end(), [](long diff) { return diff == 0; });
+	if ( !all_zeros) {
+		solve_rec_part2(differences);
+	}
+	else {
+		differences.insert(differences.begin(), 0);
+	}
+
+	auto first_value = values.front();
+	auto first_difference = differences.front();
+	values.insert(values.begin(), first_value - first_difference);
+}
+
+void
+part2()
+{
+	auto lines = read_file("data/day09.txt");
+
+	long sum = 0;
+	for ( const auto& line: lines ) {
+		auto values = read_ints(line);
+		solve_rec_part2(values);
+		sum += values.front();
+	}
+	cout << sum << endl;
+}
+
+int
+main()
+{
+	part1();
+	part2();
+}
-- 
cgit v1.3