From 756f22d58bb198b8f34589c112e1003614ccdcd6 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Sun, 2 Nov 2025 21:41:58 +0100
Subject: aoc 2017, days 1-20

---
 2017/src/day10.cpp | 124 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 124 insertions(+)
 create mode 100644 2017/src/day10.cpp

(limited to '2017/src/day10.cpp')

diff --git a/2017/src/day10.cpp b/2017/src/day10.cpp
new file mode 100644
index 0000000..d300a06
--- /dev/null
+++ b/2017/src/day10.cpp
@@ -0,0 +1,124 @@
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <numeric>
+#include <sstream>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+string
+read_file(const filesystem::path& filename)
+{
+	ifstream file{ filename };
+	string   line;
+	getline(file, line);
+	return line;
+}
+
+vector<size_t>
+split(const string& line)
+{
+	stringstream   strm{ line };
+	vector<size_t> data;
+
+	for ( string word; getline(strm, word, ','); ) {
+		data.emplace_back(stoul(word));
+	}
+
+	return data;
+}
+
+vector<unsigned>
+gen_data(size_t len)
+{
+	vector<unsigned> data(len);
+	iota(data.begin(), data.end(), 0UL);
+	return data;
+}
+
+void
+reverse(vector<unsigned>& data, size_t start, size_t len)
+{
+	auto end = start + len;
+
+	while ( start < end ) {
+		swap(data.at(start++ % data.size()), data.at(--end % data.size()));
+	}
+}
+
+void
+hash(vector<unsigned>& data, const vector<size_t>& lengths)
+{
+	size_t pos = 0;
+	for ( size_t skip = 0; skip != lengths.size(); ++skip ) {
+		reverse(data, pos, lengths.at(skip));
+		pos += lengths.at(skip) + skip;
+	}
+}
+
+void
+part1(size_t len, const string& line)
+{
+	auto data    = gen_data(len);
+	auto lengths = split(line);
+
+	hash(data, lengths);
+
+	cout << "Part1: " << data.at(0) * data.at(1) << '\n';
+}
+
+void
+hash64(vector<unsigned>& data, const vector<size_t>& lengths)
+{
+	size_t pos  = 0;
+	size_t skip = 0;
+	for ( size_t i = 0; i != 64; ++i ) {
+		for ( auto length: lengths ) {
+			reverse(data, pos, length);
+			pos += length + skip;
+			++skip;
+		}
+	}
+}
+
+void
+part2(string line)
+{
+	line += char(17);
+	line += char(31);
+	line += char(73);
+	line += char(47);
+	line += char(23);
+
+	vector<size_t> lengths;
+	for ( const auto byte: line ) {
+		lengths.emplace_back(static_cast<unsigned char>(byte));
+	}
+
+	auto data = gen_data(256);
+	hash64(data, lengths);
+
+	cout << "Part2: ";
+	for ( size_t i = 0; i != 256; i += 16 ) {
+		size_t value = 0;
+		for ( size_t j = 0; j != 16; ++j ) {
+			value ^= data.at(i + j);
+		}
+		cout << setw(2) << setfill('0') << hex << (value & 0xFF);
+	}
+	cout << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+	auto line = read_file("data/day10.txt");
+	part1(256, line);
+	part2(line);
+}
-- 
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