From d396dc3221fcf893c885bd9a370b9a30f25b31dd Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Sun, 12 Jan 2025 17:36:26 +0100
Subject: aoc 2016, days 4, 5, 6

---
 2016/src/day04.cpp | 102 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 102 insertions(+)
 create mode 100644 2016/src/day04.cpp

(limited to '2016/src/day04.cpp')

diff --git a/2016/src/day04.cpp b/2016/src/day04.cpp
new file mode 100644
index 0000000..713b16f
--- /dev/null
+++ b/2016/src/day04.cpp
@@ -0,0 +1,102 @@
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <regex>
+#include <set>
+#include <sstream>
+#include <string>
+#include <tuple>
+#include <vector>
+
+using namespace std;
+
+vector<string>
+split(const string& line, const regex& sep)
+{
+	return { sregex_token_iterator(line.begin(), line.end(), sep, -1), {} };
+}
+
+vector<tuple<vector<string>, long, string>>
+read_file(string_view filename)
+{
+	fstream input{ filename };
+
+	vector<tuple<vector<string>, long, string>> result;
+
+	for ( string line; getline(input, line); ) {
+		static const regex sep{ "[\\[\\]-]" };
+
+		auto parts = split(line, sep);
+
+		auto checksum = parts.at(parts.size() - 1);
+		parts.pop_back();
+
+		auto selector = stol(parts.at(parts.size() - 1));
+		parts.pop_back();
+
+		result.emplace_back(parts, selector, checksum);
+	}
+
+	return result;
+}
+
+void
+part1(const vector<tuple<vector<string>, long, string>>& data)
+{
+	long sum = 0;
+	for ( const auto& [ids, selector, checksum]: data ) {
+		map<char, long> counts;
+		for ( const auto& id: ids ) {
+			for ( const auto chr: id ) {
+				++counts[chr];
+			}
+		}
+
+		set<tuple<long, char>> tops;
+		for ( const auto& [chr, count]: counts ) {
+			tops.emplace(-count, chr);
+		}
+
+		string result;
+		for ( const auto& [count, chr]: tops ) {
+			result += chr;
+		}
+
+		if ( result.starts_with(checksum) ) {
+			sum += selector;
+		}
+	}
+	cout << sum << endl;
+}
+
+void
+part2(const vector<tuple<vector<string>, long, string>>& lines)
+{
+	auto rot = [](string str, int n) {
+		for ( auto& chr: str ) {
+			chr = ((chr - 'a' + n) % 26) + 'a';
+		}
+		return str;
+	};
+
+	auto is_northpole = [&](const string& str, int n) {
+		return rot(str, n) == "northpole";
+	};
+
+	for ( const auto& line: lines ) {
+		const auto& ids      = get<0>(line);
+		const auto  selector = get<1>(line);
+		if ( ranges::any_of(ids, [&](auto& str) { return is_northpole(str, (int) selector); }) ) {
+			cout << selector << endl;
+			return;
+		}
+	}
+}
+
+int
+main()
+{
+	auto data = read_file("data/day04.txt");
+	part1(data);
+	part2(data);
+}
-- 
cgit v1.3