1 files changed, 145 insertions, 0 deletions

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);
+}