Merge pull request #153 from naviqore/145-bug-non-pareto-optimal-solu…

…tion

145 bug non pareto optimal solution

src/main/java/ch/naviqore/raptor/router/LabelPostprocessor.java

@@ -70,11 +70,12 @@ List<Connection> reconstructParetoOptimalSolutions(List<QueryState.Label[]> best
                                                        Map<Integer, Integer> targetStops, LocalDate referenceDate) {
         final List<Connection> connections = new ArrayList<>();
 
+        int bestTime = timeType == TimeType.DEPARTURE ? INFINITY : -INFINITY;
+
         // iterate over all rounds
         for (QueryState.Label[] labels : bestLabelsPerRound) {
 
             QueryState.Label label = null;
-            int bestTime = timeType == TimeType.DEPARTURE ? INFINITY : -INFINITY;
 
             for (Map.Entry<Integer, Integer> entry : targetStops.entrySet()) {
                 int targetStopIdx = entry.getKey();

src/main/java/ch/naviqore/raptor/router/QueryState.java

@@ -111,14 +111,22 @@ int getComparableBestTime(int stopIdx) {
      * different label types (transfer vs. route), as the same stop transfer time is not considered.
      */
     int getActualBestTime(int stopIdx) {
-        for (int i = bestLabelsPerRound.size() - 1; i >= 0; i--) {
-            Label label = bestLabelsPerRound.get(i)[stopIdx];
+        int best_time = (timeType == TimeType.DEPARTURE) ? INFINITY : -INFINITY;
+
+        // because range raptor potentially fills target times in higher rounds which are not the best solutions, every
+        // round has to be looked at.
+        for (Label[] labels : bestLabelsPerRound) {
+            Label label = labels[stopIdx];
             if (label != null) {
-                return label.targetTime;
+                if (timeType == TimeType.DEPARTURE) {
+                    best_time = Math.min(best_time, label.targetTime);
+                } else {
+                    best_time = Math.max(best_time, label.targetTime);
+                }
             }
         }
 
-        return (timeType == TimeType.DEPARTURE) ? INFINITY : -INFINITY;
+        return best_time;
     }
 
     /**

src/test/java/ch/naviqore/raptor/router/RangeRaptorTest.java

@@ -18,6 +18,7 @@ public class RangeRaptorTest {
 
     private static final String STOP_A = "A";
     private static final String STOP_I = "I";
+    private static final String STOP_K = "K";
     private static final String STOP_N = "N";
 
     private static final LocalDateTime START_OF_DAY = LocalDateTime.of(2021, 1, 1, 0, 0);
@@ -261,6 +262,53 @@ void findArrivalConnections_withSourceTransferFirst() {
                 STOP_A, STOP_N);
     }
 
+    @Test
+    void ensureParetoOptimalConnections() {
+        // this test is based on a previous bug, where the range raptor router returned connections which were not
+        // pareto optimal (later arrival time and more rounds). This is owed to the fact that the range raptor spawns
+        // at different time points (range offsets) and potentially finds earliest arrival connections for the given
+        // offset with more rounds than the final best arrival time.
+        // this test reproduces this case by introducing a low frequency fast connection and a high frequency slower
+        // connection.
+
+        int headwayRoute1 = 15;
+        int headwayRoute2 = 60;
+        int headwayRoute3and4 = 5;
+
+        int dwellTime = 0; // simplification to better calculate times by hand
+
+        RaptorAlgorithm rangeRaptor = new RaptorRouterTestBuilder().withAddRoute1_AG(
+                        RaptorRouterTestBuilder.DEFAULT_OFFSET, headwayRoute1,
+                        RaptorRouterTestBuilder.DEFAULT_TIME_BETWEEN_STOPS, dwellTime)
+                .withAddRoute2_HL(RaptorRouterTestBuilder.DEFAULT_OFFSET, headwayRoute2,
+                        RaptorRouterTestBuilder.DEFAULT_TIME_BETWEEN_STOPS, dwellTime)
+                .withAddRoute3_MQ(RaptorRouterTestBuilder.DEFAULT_OFFSET, headwayRoute3and4,
+                        RaptorRouterTestBuilder.DEFAULT_TIME_BETWEEN_STOPS, dwellTime)
+                .withAddRoute4_RS(RaptorRouterTestBuilder.DEFAULT_OFFSET, headwayRoute3and4,
+                        RaptorRouterTestBuilder.DEFAULT_TIME_BETWEEN_STOPS, dwellTime)
+                .withSameStopTransferTime(0)
+                .withRaptorRange(900) // departures at 08:00 and 08:15
+                .withMaxDaysToScan(1)
+                .build();
+
+        // departure at 8:00 will yield only one fastest connection
+        // 08:00 A --> R1 --> 08:05 B
+        // 08:05 B --> R2 --> 08:20 K
+        LocalDateTime expectedDepartureTime = EIGHT_AM;
+        LocalDateTime expectedArrivalTime = expectedDepartureTime.plusMinutes(20);
+
+        // however since spawning at 08:15 (first range checked) will find following best solution, this test must
+        // ensure that this connection is not returned as it is not pareto optimal.
+        // 08:15 A --> R1 --> 08:40 F
+        // 08:40 F --> R4 --> 08:45 P
+        // 08:45 P --> R3 --> 09:00 K
+        List<Connection> connections = RaptorRouterTestHelpers.routeEarliestArrival(rangeRaptor, STOP_A, STOP_K,
+                EIGHT_AM);
+        assertEquals(1, connections.size());
+        RangeRaptorHelpers.assertConnection(connections.getFirst(), expectedDepartureTime, expectedArrivalTime, 2,
+                STOP_A, STOP_K);
+    }
+
     static class RangeRaptorHelpers {
 
         static void assertConnection(Connection connection, LocalDateTime expectedDepartureTime,

src/test/java/ch/naviqore/raptor/router/RaptorRouterTestBuilder.java

@@ -160,6 +160,11 @@ public RaptorRouterTestBuilder withAddRoute4_RS() {
         return this;
     }
 
+    public RaptorRouterTestBuilder withAddRoute4_RS(int offset, int headway, int travelTime, int dwellTime) {
+        routes.add(new Route("R4", List.of("R", "P", "F", "S"), offset, headway, travelTime, dwellTime));
+        return this;
+    }
+
     public RaptorRouterTestBuilder withAddRoute5_AH_selfIntersecting() {
         routes.add(new Route("R5", List.of("A", "B", "C", "D", "E", "F", "P", "O", "N", "K", "J", "I", "B", "H")));
         return this;