From 8c96639ec1f6757570510fc27f1c5fabece35eaf Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Sun, 16 Nov 2025 13:23:34 +0100
Subject: aoc 2018, days 1-11

---
 2018/src/day02.cpp | 87 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 2018/src/day02.cpp

(limited to '2018/src/day02.cpp')

diff --git a/2018/src/day02.cpp b/2018/src/day02.cpp
new file mode 100644
index 0000000..5dc6c7f
--- /dev/null
+++ b/2018/src/day02.cpp
@@ -0,0 +1,87 @@
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <set>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+vector<string>
+read_lines(const filesystem::path& filename)
+{
+	ifstream       file{ filename };
+	vector<string> lines;
+
+	for ( string line; getline(file, line); ) {
+		lines.emplace_back(line);
+	}
+
+	return lines;
+}
+
+void
+part1(const vector<string>& lines)
+{
+	int twos   = 0;
+	int threes = 0;
+	for ( const auto& line: lines ) {
+		map<char, int> foo;
+		for ( const auto chr: line ) {
+			foo[chr]++;
+		}
+
+		set<int> counts;
+		for ( const auto& [chr, count]: foo ) {
+			counts.insert(count);
+		}
+
+		if ( counts.contains(2) ) {
+			++twos;
+		}
+		if ( counts.contains(3) ) {
+			++threes;
+		}
+	}
+	cout << "Part 1: " << twos * threes << '\n';
+}
+
+void
+part2(const vector<string>& lines)
+{
+	for ( size_t i = 0; i != lines.size(); ++i ) {
+		for ( size_t j = i + 1; j != lines.size(); ++j ) {
+			const auto& lhs = lines.at(i);
+			const auto& rhs = lines.at(j);
+
+			if ( lhs.length() != rhs.length() ) {
+				throw runtime_error("invalid data");
+			}
+
+			string result;
+			for ( size_t k = 0; k != lhs.length(); ++k ) {
+				if ( lhs[k] == rhs[k] ) {
+					result += lhs[k];
+				}
+			}
+
+			if ( result.length() + 1 == lhs.length() ) {
+				cout << "Part 2: " << result << '\n';
+				return;
+			}
+		}
+	}
+}
+
+} // namespace
+
+int
+main()
+{
+	auto lines = read_lines("data/day02.txt");
+	part1(lines);
+	part2(lines);
+}
-- 
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