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/day07.cpp | 145 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 145 insertions(+)
 create mode 100644 2017/src/day07.cpp

(limited to '2017/src/day07.cpp')

diff --git a/2017/src/day07.cpp b/2017/src/day07.cpp
new file mode 100644
index 0000000..899375d
--- /dev/null
+++ b/2017/src/day07.cpp
@@ -0,0 +1,145 @@
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <numeric>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+struct Node {
+	int              weight;
+	optional<string> parent;
+	vector<string>   children;
+};
+
+vector<string>
+split(const string& line, const string& delimiters)
+{
+	vector<string> result;
+
+	size_t start = 0;
+	size_t end   = 0;
+
+	while ( (end = line.find_first_of(delimiters, start)) != string::npos ) {
+		if ( end != start ) {
+			result.emplace_back(line.substr(start, end - start));
+		}
+
+		start = end + 1;
+	}
+
+	if ( start != line.size() ) {
+		result.emplace_back(line.substr(start));
+	}
+
+	return result;
+}
+
+map<string, Node>
+read_file(const filesystem::path& filename)
+{
+	ifstream file{ filename };
+
+	map<string, Node> data; // name -> (weight, parent)
+
+	for ( string line; getline(file, line); ) {
+		const auto  parts  = split(line, " ()->,");
+		const auto& parent = parts.at(0);
+
+		data[parent].weight = stoi(parts.at(1));
+
+		for ( size_t idx = 2; idx != parts.size(); ++idx ) {
+			const auto& child  = parts.at(idx);
+			data[child].parent = parent;
+			data[parent].children.emplace_back(child);
+		}
+	}
+
+	return data;
+}
+
+string
+root_node(const map<string, Node>& data)
+{
+	for ( const auto& [name, node]: data ) {
+		if ( !node.parent ) {
+			return name;
+		}
+	}
+	throw runtime_error("no root found");
+}
+
+void
+part1(const map<string, Node>& data)
+{
+	cout << "Part1: " << root_node(data) << '\n';
+}
+
+int
+calculate_weight(const map<string, Node>& data, const string& name) // NOLINT
+{
+	const auto& node = data.at(name);
+
+	if ( node.children.empty() ) {
+		return node.weight;
+	}
+
+	int total_weight = node.weight;
+
+	map<string, int> child_weights;
+	for ( const auto& child: node.children ) {
+		auto child_weight = calculate_weight(data, child);
+		child_weights.emplace(child, child_weight);
+		total_weight += child_weight;
+	}
+
+	map<int, vector<string>> grouped;
+	for ( const auto& [child, weight]: child_weights ) {
+		grouped[weight].emplace_back(child);
+	}
+
+	if ( grouped.size() != 1 ) {
+		int    wrong_weight{};
+		int    correct_weight{};
+		string wrong_name;
+
+		for ( const auto& [weight, names]: grouped ) {
+			if ( names.size() == 1 ) {
+				wrong_weight = weight;
+				wrong_name   = names.front();
+			}
+			else {
+				correct_weight = weight;
+			}
+		}
+
+		const auto& wrong_node = data.at(wrong_name);
+		auto        diff       = wrong_weight - correct_weight;
+
+		cout << "Part2: " << wrong_node.weight - diff << '\n';
+
+		exit(0);
+	}
+
+	return total_weight;
+}
+
+void
+part2(const map<string, Node>& data)
+{
+	auto node = root_node(data);
+	calculate_weight(data, node);
+}
+
+} // namespace
+
+int
+main()
+{
+	auto data = read_file("data/day07.txt");
+	part1(data);
+	part2(data);
+}
-- 
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