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/day05.cpp | 101 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 101 insertions(+)
 create mode 100644 2018/src/day05.cpp

(limited to '2018/src/day05.cpp')

diff --git a/2018/src/day05.cpp b/2018/src/day05.cpp
new file mode 100644
index 0000000..9de484d
--- /dev/null
+++ b/2018/src/day05.cpp
@@ -0,0 +1,101 @@
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <string>
+
+using namespace std;
+
+namespace {
+
+string
+read_line(const filesystem::path& filename)
+{
+	ifstream file{ filename };
+	string   line;
+	getline(file, line);
+	return line;
+}
+
+bool
+xorEqual(char lhs, char rhs)
+{
+	return (lhs ^ (1 << 5)) == rhs;
+}
+
+#if 0
+void
+part1(string str)
+{
+	size_t idx = 1;
+	while ( idx < str.length() ) {
+		if ( xorEqual(str[idx - 1], str[idx]) ) {
+			str.erase(idx - 1, 2);
+			idx = 1;
+		}
+		else {
+			++idx;
+		}
+	}
+
+	cout << "Part 1: " << str.length() << '\n';
+}
+#endif
+
+void
+part1_opti(string_view str)
+{
+	string result;
+
+	for ( const auto chr: str ) {
+		if ( !result.empty() && xorEqual(result.back(), chr) ) {
+			result.pop_back();
+		}
+		else {
+			result.push_back(chr);
+		}
+	}
+
+	cout << "Part 1: " << result.length() << '\n';
+}
+
+void
+part2(string_view str)
+{
+	size_t min_length = str.size();
+	for ( auto ch = 'a'; ch != 'z'; ++ch ) {
+		string result;
+
+		for ( const auto chr: str ) {
+			if ( tolower(chr) == ch ) {
+				// nichts
+			}
+			else if ( !result.empty() && xorEqual(result.back(), chr) ) {
+				result.pop_back();
+			}
+			else {
+				result.push_back(chr);
+			}
+		}
+		min_length = min(min_length, result.length());
+	}
+
+	cout << "Part 2: " << min_length << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+	auto line = read_line("data/day05.txt");
+	// part1(line);
+	part1_opti(line);
+	part2(line);
+	/*
+	cout << reduce("aA") << '\n';
+	cout << reduce("abBA") << '\n';
+	cout << reduce("abAB") << '\n';
+	cout << reduce("aabAAB") << '\n';
+	cout << reduce("dabAcCaCBAcCcaDA") << '\n';
+	*/
+}
-- 
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