Improved documentation of code and fixed perf bug

include/flight_planner.h

@@ -30,10 +30,11 @@ class IdCity {
   bool operator!=(const IdCity& other) const { return !(*this == other); }
   bool operator<(const IdCity& other) const { return id_ < other.id_; }
 
+  /// Returns the id of the city
   int id() const { return id_; }
 
  private:
-  int id_;
+  int id_;  // Id of the city
 };
 
 
@@ -46,6 +47,8 @@ class StateAircraft {
     id_city_(id_city), battery_level_hours_(battery_level_hours) {}
   StateAircraft() : id_city_(IdCity()), battery_level_hours_(-1.0) {}
 
+  /// Calculates the change in battery flying time from this state to another state
+  ///   DeltaBattery = BatteryOther - BatteryThis
   double CalcBatteryDelta(const StateAircraft& other) const {
     assert(id_city_ == other.id_city_);
     return other.battery_level_hours_ - battery_level_hours_;
@@ -63,12 +66,15 @@ class StateAircraft {
     }
   }
 
+  /// Returns the id of the city
   IdCity id_city() const { return id_city_; }
+
+  /// Returns the remaining battery flight time in hours
   double battery_level_hours() const { return battery_level_hours_; }
 
  private:
-  IdCity id_city_;
-  double battery_level_hours_;
+  IdCity id_city_;  // Id of the city
+  double battery_level_hours_;  // Remaining battery flight time in hours
 };
 
 
@@ -105,6 +111,9 @@ class FlightPlannerBase : public GraphDirected<StateAircraft> {
   }
 
   static constexpr double MinBatteryHours() { return 0.0; }
+
+  /// Returns the maximum battery flytime in hours. The maximum flytime is the
+  /// maximum flight distance 320km divided by the speed of the aircraft.
   static constexpr double MaxBatteryHours() { return 320.0 / SpeedKmPerHr(); }
   static constexpr double MaxFlightTimeHours() { return MaxBatteryHours() - MinBatteryHours(); }
 
@@ -137,7 +146,7 @@ class FlightPlannerBase : public GraphDirected<StateAircraft> {
   double CalcChargeRateKmPerHr(const IdCity& id_city) const { return GetAirport(id_city).rate; }
 
   static constexpr double RadEarth() { return 6356.752; }  // Radius of Earth in km
-  static constexpr double SpeedKmPerHr() { return 105.0; }  // Speed of aircraft in km/hr
+  static constexpr double SpeedKmPerHr() { return 105.0; }  // Speed of aircraft in km/hr from the problem statement
 
   const std::array<row, 303> airports_;  // List of airports copied from the non-constant global in airports.h
 };
@@ -153,6 +162,7 @@ class FlightPlannerExact : public FlightPlannerBase {
   }
 
  private:
+  // Adds edges for this graph construction approach
   void AddEdgesFlightsExact();
 };
 
@@ -170,10 +180,14 @@ class FlightPlannerGrid : public FlightPlannerBase {
     AddEdgesCharge();
   }
 
+  /// Returns the number of battery levels in the grid
   int n_levels() const { return n_levels_; }
+
+  /// Returns the vector of evenly spaced battery levels
   const vector<double>& v_battery_levels() const { return v_battery_levels_; }
 
  private:
+  // Creates a vector of evenly spaced battery levels between the minimum and maximum battery levels
   static vector<double> CreateGridBatteryLevels(int n_levels) {
     const double delta_battery = (MaxBatteryHours() - MinBatteryHours()) / (n_levels - 1);
 
@@ -186,14 +200,17 @@ class FlightPlannerGrid : public FlightPlannerBase {
     return v_battery_levels;
   }
 
+  // Adds vertices linearly spaced between the minimum and maximum battery levels
   void AddVerticesGrid();
 
+  // Finds the battery level in the grid that is closest to the given battery level
   int FindBatteryLevel(const double battery_level) const;
 
+  // Adds approximate edges for this graph construction approach
   void AddEdgesDrivingGrid();
 
-  const int n_levels_;
-  const vector<double> v_battery_levels_;
+  const int n_levels_;  // Number of evenly spaced battery levels in the grid
+  const vector<double> v_battery_levels_;  // Vector of evenly spaced battery levels
 };
 
 };  // namespace std

include/graph_directed.h

@@ -103,7 +103,10 @@ class GraphDirected {
     return make_pair(path, dist[dst]);  // Return the shortest path and its cost
   }
 
+  /// Returns the set of vertices in the graph
   const set<VertexType>& vertices() const { return vertices_; }
+
+  /// Returns the adjacency list of the graph
   const map<VertexType, map<VertexType, double>>& adjacency_list() const { return adjacency_list_; }
 
  private:

src/flight_planner.cpp

@@ -6,13 +6,9 @@ namespace std {
 // FlightPlannerBase
 
 pair<vector<StateAircraft>, double> FlightPlannerBase::SolvePath(const char* char_src, const char* char_dst) const {
-  IdCity id_src = GetIdCity(char_src);
-  IdCity id_dst = GetIdCity(char_dst);
-
-  // Calculate shortest distance from vertex src to every other vertex
-  StateAircraft src{id_src, MaxBatteryHours()};  // Source city with fully battery
-  StateAircraft dst{id_dst, MinBatteryHours()};  // Destination city
-  return CalcMinCostPathDijkstra(src, dst);
+  StateAircraft src{GetIdCity(char_src), MaxBatteryHours()};  // Source city with fully battery
+  StateAircraft dst{GetIdCity(char_dst), MinBatteryHours()};  // Destination city
+  return CalcMinCostPathDijkstra(src, dst);                   // Solve for the minimum cost path
 }
 
 void FlightPlannerBase::AddEdgesCharge() {
@@ -39,7 +35,7 @@ void FlightPlannerBase::AddEdgesCharge(const IdCity& id_city, const set<StateAir
     if (next_it != vertex_states.end()) {
       StateAircraft next_vertex_state = *next_it;
 
-      double charge_time = CalcChargeTime(vertex_state, next_vertex_state);
+      const double charge_time = CalcChargeTime(vertex_state, next_vertex_state);
 
       // Represents charging edge
       AddDirectedEdge(vertex_state, next_vertex_state, charge_time);
@@ -60,40 +56,43 @@ IdCity FlightPlannerBase::GetIdCity(const string& name) const {
 }
 
 void FlightPlannerBase::PrintPath(const vector<StateAircraft>& v_path) const {
-  IdCity id_src = v_path[0].id_city();
-  IdCity id_dst = v_path[v_path.size() - 1].id_city();
+  IdCity id_src = v_path[0].id_city();                  // Id of the first city
+  IdCity id_dst = v_path[v_path.size() - 1].id_city();  // Id of the last city
 
   cout << endl;
   PrintCity(id_src); cout << ", " << endl;      // Print first city
-  PrintChargingCitiesAndTimes(v_path, id_dst);  // Print out each city the plane charges at
+  PrintChargingCitiesAndTimes(v_path, id_dst);  // Print out each intermediate city and charging time
   PrintCity(id_dst);                            // Print last city
   cout << endl;
 }
 
 void FlightPlannerBase::PrintChargingCitiesAndTimes(const vector<StateAircraft>& v_path, const IdCity& id_dst) const {
-  auto fn_find_last_index_of_city = [this](vector<StateAircraft> v_path, int i) {
-    int j = i;
-    while (j < v_path.size() && v_path[i].id_city() == v_path[j].id_city()) {
-      j++;
+  // Finds the index where charging stops
+  auto fn_find_i_stop = [this](const vector<StateAircraft>& v_path, int i_start) {
+    int i_stop = i_start;
+    while (v_path[i_start].id_city() == v_path[i_stop].id_city()) {  // Is same city
+      i_stop++;
+      if (i_stop == v_path.size()) { break; }  // Reached the end of the path
     }
-    return j - 1;
+
+    return i_stop - 1;  // The last index before the city changes
   };
 
   // Prints out the change time
-  auto fn_print_charge_time = [this](vector<StateAircraft> v_path, int i, int j) {
-    PrintCity(v_path[i]);
-    double charge_time_hours = CalcChargeTime(v_path[i], v_path[j]);
+  auto fn_print_charge_time = [this](vector<StateAircraft> v_path, int i_arrive, int i_depart) {
+    PrintCity(v_path[i_arrive]);
+    double charge_time_hours = CalcChargeTime(v_path[i_arrive], v_path[i_depart]);
     cout << ", " << setprecision(16) << charge_time_hours << "," << endl;
   };
 
   // Runs the lambda on each city the plane charges at
-  int ind_arrive = 1;
-  int ind_depart = -1;
+  int i_charge_start = 1;
+  int i_charge_stop = -1;
 
-  while (v_path[ind_arrive].id_city() != id_dst) {
-    ind_depart = fn_find_last_index_of_city(v_path, ind_arrive);
-    fn_print_charge_time(v_path, ind_arrive, ind_depart);
-    ind_arrive = ind_depart + 1;
+  while (v_path[i_charge_start].id_city() != id_dst) {
+    i_charge_stop = fn_find_i_stop(v_path, i_charge_start);
+    fn_print_charge_time(v_path, i_charge_start, i_charge_stop);
+    i_charge_start = i_charge_stop + 1;  // Start at the next city
   }
 }
 
@@ -105,23 +104,25 @@ pair<double, double> FlightPlannerBase::GetLatLonRadians(const IdCity& id_city)
 }
 
 double FlightPlannerBase::CalcDistKm(const IdCity& src, const IdCity& dst) const {
-  double lat1r, lon1r, lat2r, lon2r, u, v;
+  const auto lat1r_lon1r = GetLatLonRadians(src);
+  const double lat1r = lat1r_lon1r.first;
+  const double lon1r = lat1r_lon1r.second;
 
-  // Get the latitude and longitude of the source and destination cities in radians
-  tie(lat1r, lon1r) = GetLatLonRadians(src);
-  tie(lat2r, lon2r) = GetLatLonRadians(dst);
+  const auto lat2r_lon2r = GetLatLonRadians(dst);
+  const double lat2r = lat2r_lon2r.first;
+  const double lon2r = lat2r_lon2r.second;
 
   // Copilot auto-generated code
-  u = sin((lat2r - lat1r) / 2);
-  v = sin((lon2r - lon1r) / 2);
+  const double u = sin((lat2r - lat1r) / 2);
+  const double v = sin((lon2r - lon1r) / 2);
   return 2.0 * RadEarth() * asin(sqrt(u * u + cos(lat1r) * cos(lat2r) * v * v));
 }
 
 double FlightPlannerBase::CalcChargeTime(const StateAircraft& state_lo, const StateAircraft& state_hi) const {
   const IdCity& id = state_lo.id_city();
-  assert(id == state_hi.id_city());  // Charging needs to happen at the same city
+  assert(id == state_hi.id_city());  // Aircraft can't change cities while charging
 
-  const double flight_time_per_charge_hr = CalcChargeRateKmPerHr(id) / SpeedKmPerHr();
+  const double flight_time_per_charge_hr = CalcChargeRateKmPerHr(id) / SpeedKmPerHr();  // Called R in the readme
   return state_lo.CalcBatteryDelta(state_hi) / flight_time_per_charge_hr;
 }
 
@@ -138,13 +139,16 @@ void FlightPlannerExact::AddEdgesFlightsExact() {
 
       double flight_time = CalcFlightTimeHours(src, dst);
       if (flight_time < MaxFlightTimeHours()) {
-        // Flight that departs with full charge
-        double max_battery = MaxBatteryHours();
-        AddDirectedEdge(StateAircraft{src, max_battery}, StateAircraft{dst, max_battery - flight_time}, flight_time);
-
-        // Flight that arrives with zero charge
-        double min_battery = MinBatteryHours();
-        AddDirectedEdge(StateAircraft{src, flight_time + min_battery}, StateAircraft{dst, min_battery}, flight_time);
+        {
+          // Flight that departs with full charge
+          double max_battery = MaxBatteryHours();
+          AddDirectedEdge(StateAircraft{src, max_battery}, StateAircraft{dst, max_battery - flight_time}, flight_time);
+        }
+        {
+          // Flight that arrives with zero charge
+          double min_battery = MinBatteryHours();
+          AddDirectedEdge(StateAircraft{src, flight_time + min_battery}, StateAircraft{dst, min_battery}, flight_time);
+        }
       }
     }
   }
@@ -161,6 +165,7 @@ void FlightPlannerGrid::AddVerticesGrid() {
   }
 }
 
+// Finds the nearest battery level without going over
 int FlightPlannerGrid::FindBatteryLevel(const double battery_level) const {
   const vector<double>& v_bat = v_battery_levels();
 
@@ -177,14 +182,14 @@ void FlightPlannerGrid::AddEdgesDrivingGrid() {
   for (auto vertex_i : vertices()) {
     for (int j = 0; j < NumAirports(); j++) {
       if (vertex_i.id_city() == IdCity{j}) { continue; }
-      double flight_time_ij = CalcFlightTimeHours(vertex_i.id_city(), IdCity{j});
-      double battery_i = vertex_i.battery_level_hours();
-      double battery_post = battery_i - flight_time_ij;
-      double battery_min = MinBatteryHours();
+      const double flight_time_ij = CalcFlightTimeHours(vertex_i.id_city(), IdCity{j});
+      const double battery_i = vertex_i.battery_level_hours();
+      const double battery_post = battery_i - flight_time_ij;
+      const double battery_min = MinBatteryHours();
 
       if (battery_post < battery_min) { continue; }
-      int ind_lo = FindBatteryLevel(battery_post);
-      double battery_level_lo = v_battery_levels()[ind_lo];
+      const int ind_lo = FindBatteryLevel(battery_post);
+      const double battery_level_lo = v_battery_levels()[ind_lo];
       StateAircraft vertex_j_lo{IdCity{j}, battery_level_lo};
       AddDirectedEdge(vertex_i, vertex_j_lo, flight_time_ij);
     }

src/main.cpp

@@ -11,8 +11,8 @@ int main(int argc, char** argv) {
     return 1;
   }
 
-  FlightPlannerExact(airports).SolvePathAndPrint(argv[1], argv[2]);
-  // FlightPlannerGrid(airports, 4).SolvePathAndPrint(argv[1], argv[2]);
+  FlightPlannerExact(airports).SolvePathAndPrint(argv[1], argv[2]);  // Run the exact planner
+  // FlightPlannerGrid(airports, 4).SolvePathAndPrint(argv[1], argv[2]);  // Run the grid planner
 
   return 0;
 };