From 56e890cec0a28c0a485212ccebfaf774235a79a2 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Wed, 3 Jan 2024 23:35:54 +0100
Subject: prepare for more puzzles ... :)

---
 2023/src/day03.cpp | 174 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 174 insertions(+)
 create mode 100644 2023/src/day03.cpp

(limited to '2023/src/day03.cpp')

diff --git a/2023/src/day03.cpp b/2023/src/day03.cpp
new file mode 100644
index 0000000..b266f59
--- /dev/null
+++ b/2023/src/day03.cpp
@@ -0,0 +1,174 @@
+#include <cctype>
+#include <fstream>
+#include <iostream>
+#include <string>
+#include <string_view>
+#include <vector>
+
+using namespace std;
+
+vector<string>
+read_file(string_view filename)
+{
+	fstream        input{ filename };
+	vector<string> data;
+
+	for ( string line; getline(input, line); ) {
+		data.emplace_back(line);
+	}
+
+	return data;
+}
+
+bool
+is_digit(char chr)
+{
+	return std::isdigit(static_cast<unsigned char>(chr)) != 0;
+}
+
+vector<tuple<size_t, size_t>>
+positions(size_t row, size_t col)
+{
+	return {
+		{ row - 1, col - 1 },
+		{ row - 0, col - 1 },
+		{ row + 1, col - 1 },
+
+		{ row - 1, col },
+		{ row + 1, col },
+
+		{ row - 1, col + 1 },
+		{ row - 0, col + 1 },
+		{ row + 1, col + 1 },
+	};
+}
+
+void
+part1() // NOLINT
+{
+	auto lines = read_file("data/day03.txt");
+
+	auto is_symbol = [&lines](size_t row, size_t col) -> bool {
+		static const string symbols{ "*#+$%=-@&/" };
+
+		if ( row >= lines.size() || col >= lines[row].size() ) {
+			return false;
+		}
+
+		auto symbol = lines[row][col];
+
+		return symbols.find(symbol) != string::npos;
+	};
+
+	auto bordering = [&is_symbol](size_t row, size_t col) -> bool {
+		bool result = false;
+
+		for (const auto& position: positions(row, col)) {
+			result |= is_symbol(get<0>(position), get<1>(position));
+		}
+
+		return result;
+	};
+
+	auto sum = 0;
+	for ( size_t row = 0; row != lines.size(); ++row ) {
+		const auto& line = lines[row];
+
+		string::size_type start = 0;
+		while ( start != line.size() ) {
+			while ( start != line.size() && !is_digit(line[start]) ) {
+				++start;
+			}
+
+			auto end = start;
+			while ( end != line.size() && is_digit(line[end]) ) {
+				++end;
+			}
+
+			if ( start != end ) {
+				auto result = false;
+
+				for ( auto col = start; col != end; ++col ) {
+					result |= bordering(row, col);
+				}
+
+				if ( result ) {
+					sum += stoi(line.substr(start, end - start));
+				}
+
+				start = end;
+			}
+		}
+	}
+	cout << sum << endl;
+}
+
+void
+part2() // NOLINT
+{
+	auto lines = read_file("data/day03.txt");
+
+	auto find_integer = [](vector<string>& lines, size_t row, size_t col, int& value) -> bool { // NOLINT
+		if ( row >= lines.size() || col >= lines[row].size() ) {
+			return false;
+		}
+
+		auto& line = lines[row];
+
+		if ( !is_digit(line[col]) ) {
+			return false;
+		}
+
+		// Anfang der Zahl suchen
+		auto start = col;
+		for ( ; start != 0 && is_digit(line[start - 1]); --start ) // NOLINT
+			;
+
+		auto end = col;
+		for ( ; end != line.size() && is_digit(line[end]); ++end ) // NOLINT
+			;
+
+		value = stoi(line.substr(start, end - start));
+
+		for ( ; start != end; ++start ) {
+			line[start] = '.';
+		}
+
+		return true;
+	};
+
+	auto sum = 0;
+	for ( size_t row = 0; row != lines.size(); ++row ) {
+		const auto& line = lines[row];
+
+		auto col = line.find('*');
+		while ( col != string::npos ) {
+			vector<int> values;
+
+			auto lines_copy{ lines };
+
+			for ( const auto& position: positions(row, col) ) {
+				auto value = 0;
+
+				if ( find_integer(lines_copy, get<0>(position), get<1>(position), value) ) {
+					values.emplace_back(value);
+				}
+			}
+
+			if ( values.size() == 2 ) {
+				auto ratio = values[0] * values[1];
+				sum += ratio;
+			}
+
+			col = line.find('*', col + 1);
+		}
+	}
+	cout << sum << endl;
+}
+
+int
+main()
+{
+	part1();
+	part2();
+}
-- 
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