1 files changed, 102 insertions, 0 deletions

diff --git a/2017/src/day24.cpp b/2017/src/day24.cpp
new file mode 100644
index 0000000..fa4148c
--- /dev/null
+++ b/2017/src/day24.cpp
@@ -0,0 +1,102 @@
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <set>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+vector<tuple<long, long>>
+read_file(const filesystem::path& filename)
+{
+        ifstream                  file{ filename };
+        vector<tuple<long, long>> data;
+
+        long lhs = 0;
+        long rhs = 0;
+        char sep = 0;
+
+        while ( file >> lhs >> sep >> rhs ) {
+                data.emplace_back(lhs, rhs);
+        }
+        return data;
+}
+
+long
+strongest(const vector<tuple<long, long>>& data, long current = 0, const set<size_t>& used = {})
+{
+        long best_strength = 0;
+
+        for ( size_t i = 0; i != data.size(); ++i ) {
+                if ( used.contains(i) ) {
+                        continue;
+                }
+
+                auto [lhs, rhs] = data.at(i);
+                if ( lhs == current || rhs == current ) {
+                        auto next_port = (lhs == current) ? rhs : lhs;
+                        auto new_used{ used };
+                        new_used.emplace(i);
+                        auto strength = lhs + rhs + strongest(data, next_port, new_used);
+                        best_strength = max(best_strength, strength);
+                }
+        }
+
+        return best_strength;
+}
+
+tuple<long, size_t>
+strongest_and_longest(const vector<tuple<long, long>>& data, long current = 0, const set<size_t>& used = {})
+{
+        long   best_strength = 0;
+        size_t best_length   = 0;
+
+        for ( size_t i = 0; i != data.size(); ++i ) {
+                if ( used.contains(i) ) {
+                        continue;
+                }
+
+                auto [lhs, rhs] = data.at(i);
+                if ( lhs == current || rhs == current ) {
+                        auto next_port = (lhs == current) ? rhs : lhs;
+                        auto new_used{ used };
+                        new_used.emplace(i);
+                        auto [sub_strength, sub_length] = strongest_and_longest(data, next_port, new_used);
+
+                        auto total_strength = sub_strength + lhs + rhs;
+                        auto total_length   = sub_length + 1;
+
+                        if ( total_length > best_length || (total_length == best_length && total_strength > best_strength) ) {
+                                best_strength = total_strength;
+                                best_length   = total_length;
+                        }
+                }
+        }
+
+        return make_tuple(best_strength, best_length);
+}
+
+void
+part1(const vector<tuple<long, long>>& data)
+{
+        cout << "Part1: " << strongest(data) << '\n';
+}
+
+void
+part2(const vector<tuple<long, long>>& data)
+{
+        auto [strength, length] = strongest_and_longest(data);
+        cout << "Part2: " << strength << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+        auto data = read_file("data/day24.txt");
+        part1(data);
+        part2(data);
+}