1 files changed, 108 insertions, 0 deletions

diff --git a/2015/src/day13.cpp b/2015/src/day13.cpp
new file mode 100644
index 0000000..7256b81
--- /dev/null
+++ b/2015/src/day13.cpp
@@ -0,0 +1,108 @@
+#include <algorithm>
+#include <fstream>
+#include <iostream>
+#include <iterator>
+#include <limits>
+#include <map>
+#include <set>
+#include <sstream>
+#include <string>
+#include <tuple>
+#include <vector>
+
+using namespace std;
+
+auto
+split(const string& line, char sep = ' ')
+{
+        vector<string> parts;
+        stringstream   input{ line };
+
+        for ( string part; getline(input, part, sep); ) {
+                parts.emplace_back(part);
+        }
+
+        return parts;
+}
+
+auto
+read_file(string_view filename)
+{
+        fstream                          input{ filename };
+        set<string>                      names;
+        map<tuple<string, string>, long> table;
+
+        for ( string line; getline(input, line); ) {
+                if ( line.ends_with(".") ) {
+                        line.pop_back();
+                }
+
+                auto parts = split(line);
+
+                auto start = parts[0];
+                auto units = parts[2] == "gain" ? stol(parts[3]) : -stol(parts[3]);
+                auto end   = parts[10]; // NOLINT
+
+                table[{ start, end }] = units;
+
+                names.insert(start);
+        }
+        return table;
+}
+
+void
+part1(map<tuple<string, string>, long>& table)
+{
+        set<string> unique_names;
+        for ( const auto& item: table ) {
+                unique_names.insert(get<0>(item.first));
+        }
+        vector<string> names{ begin(unique_names), end(unique_names) };
+
+        long happiness_sofar = numeric_limits<long>::min();
+        do {
+                long happiness = 0;
+                for ( size_t idx = 0; idx != names.size(); ++idx ) {
+                        auto next_idx = (idx + 1) % names.size();
+
+                        happiness += table[{ names[idx], names[next_idx] }];
+                        happiness += table[{ names[next_idx], names[idx] }];
+                }
+
+                happiness_sofar = max(happiness_sofar, happiness);
+        } while ( next_permutation(begin(names), end(names)) );
+        cout << happiness_sofar << endl;
+}
+
+void
+part2(map<tuple<string, string>, long>& table)
+{
+        set<string> unique_names;
+        for ( const auto& item: table ) {
+                unique_names.insert(get<0>(item.first));
+        }
+        vector<string> names{ begin(unique_names), end(unique_names) };
+        names.emplace_back("Hartkode");
+
+        long happiness_sofar = numeric_limits<long>::min();
+        do {
+                long happiness = 0;
+                for ( size_t idx = 0; idx != names.size(); ++idx ) {
+                        auto next_idx = (idx + 1) % names.size();
+
+                        happiness += table[{ names[idx], names[next_idx] }];
+                        happiness += table[{ names[next_idx], names[idx] }];
+                }
+
+                happiness_sofar = max(happiness_sofar, happiness);
+        } while ( next_permutation(begin(names), end(names)) );
+        cout << happiness_sofar << endl;
+}
+
+int
+main()
+{
+        auto table = read_file("data/day13.txt");
+        part1(table);
+        part2(table);
+}