From 72253f5efb10c7892fdb09d52343764124cd717c Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Wed, 13 Dec 2023 19:15:25 +0100
Subject: Lösung für Tag 13
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---
 src/day13.cpp | 132 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 132 insertions(+)
 create mode 100644 src/day13.cpp

(limited to 'src/day13.cpp')

diff --git a/src/day13.cpp b/src/day13.cpp
new file mode 100644
index 0000000..43fd39e
--- /dev/null
+++ b/src/day13.cpp
@@ -0,0 +1,132 @@
+#include <algorithm>
+#include <fstream>
+#include <iostream>
+#include <iterator>
+#include <sstream>
+#include <string>
+#include <vector>
+using namespace std;
+
+string
+read_file(string_view filename)
+{
+	fstream input{ filename };
+	return { istreambuf_iterator<char>{ input }, istreambuf_iterator<char>{} };
+}
+
+vector<string>
+split(string_view line, string_view delimiter)
+{
+	size_t pos_start = 0;
+	size_t pos_end   = 0;
+
+	vector<string> res;
+
+	while ( (pos_end = line.find(delimiter, pos_start)) != std::string::npos ) {
+		auto token = line.substr(pos_start, pos_end - pos_start);
+		pos_start  = pos_end + delimiter.length();
+
+		res.emplace_back(token);
+	}
+
+	res.emplace_back(line.substr(pos_start));
+	return res;
+}
+
+vector<string>
+transpose(const vector<string>& input)
+{
+	vector<string> result(input[0].size());
+
+	for ( const auto& i: input ) {
+		for ( size_t j = 0; j < i.size(); j++ ) {
+			result[j] += i[j];
+		}
+	}
+	return result;
+}
+
+long
+find_mirror(const vector<string>& input)
+{
+	for ( size_t idx = 1; idx < input.size(); ++idx ) {
+		bool equal = true;
+		for ( size_t cnt = 0; cnt != min(idx, input.size() - idx); ++cnt ) {
+			auto cmp_result = (input.at(idx + cnt) == input.at(idx - 1 - cnt));
+			if ( !cmp_result ) {
+				equal = false;
+				break;
+			}
+		}
+		if ( equal ) {
+			return long(idx);
+		}
+	}
+	return 0;
+}
+
+void
+part1()
+{
+	auto contents = read_file("data/day13.txt");
+	auto parts    = split(contents, "\n\n");
+
+	long sum = 0;
+	for ( const auto& part: parts ) {
+		auto lines = split(part, "\n");
+
+		sum += find_mirror(transpose(lines));
+		sum += find_mirror(lines) * 100;
+	}
+	cout << sum << endl;
+}
+
+long
+count_differences(string_view a, string_view b) // NOLINT
+{
+	long errs = 0;
+	for (size_t idx = 0; idx != a.size(); ++idx) {
+		if (a[idx] != b[idx]) {
+			++errs;
+		}
+	}
+	return errs;
+}
+
+long
+find_mirror2(const vector<string>& input)
+{
+	for ( size_t idx = 1; idx < input.size(); ++idx ) {
+		long errs = 0;
+		for ( size_t cnt = 0; cnt != min(idx, input.size() - idx); ++cnt ) {
+			errs += count_differences(input.at(idx + cnt), input.at(idx - 1 - cnt));
+		}
+		if ( errs == 1 ) {
+			return long(idx);
+		}
+	}
+	return 0;
+}
+
+void
+part2()
+{
+	auto contents = read_file("data/day13.txt");
+	auto parts    = split(contents, "\n\n");
+
+	long sum = 0;
+	for ( const auto& part: parts ) {
+		auto lines = split(part, "\n");
+
+		sum += find_mirror2(transpose(lines));
+		sum += find_mirror2(lines) * 100;
+	}
+	cout << sum << endl;
+}
+
+int
+main()
+{
+	// part1();
+	part2();
+}
-- 
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