From aa911a88fbc47febffe88cde8087843869e9b467 Mon Sep 17 00:00:00 2001
From: Reimar <mail@reim.ar>
Date: Wed, 17 Dec 2025 09:31:46 +0100
Subject: [PATCH] Solve day 2 part 1

---
 day_2.cpp | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 day_2.cpp

diff --git a/day_2.cpp b/day_2.cpp
new file mode 100644
index 0000000..f332010
--- /dev/null
+++ b/day_2.cpp
@@ -0,0 +1,37 @@
+#include <fstream>
+#include <iostream>
+
+bool is_invalid(long int id)
+{
+	std::string id_str = std::to_string(id);
+	for (int i = 0; i < id_str.size(); i++) {
+		if (id_str.substr(0, i) + id_str.substr(0, i) == id_str) {
+			return true;
+		}
+	}
+	return false;
+}
+
+int main()
+{
+	std::ifstream file("input.txt");
+
+	long int invalid_sum = 0;
+
+	std::string range;
+	while (getline(file, range, ',')) {
+		long int range_start, range_end;
+		sscanf(range.c_str(), "%ld-%ld", &range_start, &range_end);
+
+		std::cout << "Range " << range_start << "-" << range_end << ":";
+		for (long int i = range_start; i <= range_end; i++) {
+			if (is_invalid(i)) {
+				std::cout << " " << i;
+				invalid_sum += i;
+			}
+		}
+		std::cout << std::endl;
+	}
+
+	std::cout << "Sum of invalid IDs: " << invalid_sum << std::endl;
+}