From ce66d4d5a7b67cc5a36dd4dc1a85e0c7129ea5d6 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Mon, 2 Dec 2024 19:07:29 +0100
Subject: aoc 2024, day2

---
 2024/src/day02.cpp | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)
 create mode 100644 2024/src/day02.cpp

diff --git a/2024/src/day02.cpp b/2024/src/day02.cpp
new file mode 100644
index 0000000..c8ca66f
--- /dev/null
+++ b/2024/src/day02.cpp
@@ -0,0 +1,76 @@
+#include <cstddef>
+#include <fstream>
+#include <iostream>
+#include <sstream>
+#include <string>
+#include <vector>
+using namespace std;
+
+vector<vector<long>>
+read_file(string_view filename)
+{
+	fstream              input{ filename };
+	vector<vector<long>> lines;
+
+	auto split = [](const string& str) {
+		stringstream sstr{ str };
+		vector<long> values;
+
+		for ( long value = 0; sstr >> value; ) {
+			values.emplace_back(value);
+		}
+		return values;
+	};
+
+	for ( string line; getline(input, line); ) {
+		lines.emplace_back(split(line));
+	}
+
+	return lines;
+}
+
+bool
+is_safe(const vector<long>& values)
+{
+	vector<long> diffs;
+	for ( size_t i = 1; i < values.size(); ++i ) {
+		diffs.emplace_back(values.at(i) - values.at(i - 1));
+	}
+
+	auto all_negative = ranges::all_of(diffs, [](auto diff) { return diff >= -3 && diff < 0; });
+	auto all_positive = ranges::all_of(diffs, [](auto diff) { return diff <= 3 && diff > 0; });
+
+	return all_positive || all_negative;
+}
+
+void
+part1(const vector<vector<long>>& lines)
+{
+	cout << ranges::count_if(lines, is_safe) << endl;
+}
+
+void
+part2(const vector<vector<long>>& lines)
+{
+	long safe_count = 0;
+	for ( const auto& line: lines ) {
+		auto         safe = false;
+		for ( size_t i = 0; i != line.size(); ++i ) {
+			auto copy = line;
+			copy.erase(copy.begin() + ptrdiff_t(i));
+			safe |= is_safe(copy);
+		}
+		if ( safe ) {
+			++safe_count;
+		}
+	}
+	cout << safe_count << endl;
+}
+
+int
+main()
+{
+	auto lines = read_file("data/day02.txt");
+	part1(lines);
+	part2(lines);
+}
-- 
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