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/day15.cpp | 102 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 102 insertions(+)
 create mode 100644 2023/src/day15.cpp

(limited to '2023/src/day15.cpp')

diff --git a/2023/src/day15.cpp b/2023/src/day15.cpp
new file mode 100644
index 0000000..6fcbfc2
--- /dev/null
+++ b/2023/src/day15.cpp
@@ -0,0 +1,102 @@
+#include <algorithm>
+#include <fstream>
+#include <iostream>
+#include <list>
+#include <numeric>
+#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>{} };
+}
+
+void
+rtrim(string& str)
+{
+	str.erase(find_if(str.rbegin(), str.rend(), [](auto chr) { return !isspace(chr); }).base(), str.end());
+}
+
+vector<string>
+split(const string& line, char sep)
+{
+	vector<string> parts{};
+	stringstream   input{ line };
+
+	for ( string part; getline(input, part, sep); ) {
+		rtrim(part);
+		parts.emplace_back(part);
+	}
+
+	return parts;
+}
+
+unsigned int
+calculate_hash(string_view str)
+{
+	unsigned int value = 0;
+	for ( auto chr: str ) {
+		value += static_cast<unsigned char>(chr);
+		value *= 17;
+	}
+	return value % 256;
+}
+
+void
+part1()
+{
+	const auto parts = split(read_file("data/day15.txt"), ',');
+	cout << accumulate(parts.begin(), parts.end(), 0UL, [](auto init, const auto& str) { return init + calculate_hash(str); }) << endl;
+}
+
+void
+part2()
+{
+	vector<list<tuple<string, long>>> boxes(256);
+
+	const auto line  = read_file("data/day15.txt");
+	const auto parts = split(line, ',');
+	for ( const auto& part: parts ) {
+		const auto pos  = part.find_first_of("=-");
+		const auto lens = part.substr(0, pos);
+		auto&      box  = boxes[calculate_hash(lens)];
+
+		if ( part[pos] == '=' ) {
+			const auto value = stol(part.substr(pos + 1));
+
+			auto iter = find_if(box.begin(), box.end(), [&lens](const auto& element) { return get<0>(element) == lens; });
+			if ( iter == box.end() ) {
+				box.emplace_back(lens, value);
+			}
+			else {
+				get<1>(*iter) = value;
+			}
+		}
+		else {
+			box.remove_if([&lens](const auto& element) { return get<0>(element) == lens; });
+		}
+	}
+
+	long value = 0;
+	for ( size_t idx = 0; idx != boxes.size(); ++idx ) {
+		const auto& box = boxes[idx];
+
+		long lens_number = 1;
+		for ( const auto& lens: box ) {
+			value += static_cast<long>(idx + 1) * lens_number * get<1>(lens);
+			++lens_number;
+		}
+	}
+	cout << value << endl;
+}
+
+int
+main()
+{
+	part1();
+	part2();
+}
-- 
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