Add support for complex actions

core/src/main/java/aima/core/search/basic/support/BasicBidirectionalActions.java

@@ -1,6 +1,8 @@
 package aima.core.search.basic.support;
 
 import aima.core.search.api.BidirectionalActions;
+import aima.core.search.api.SearchController;
+
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
@@ -13,10 +15,14 @@ public class BasicBidirectionalActions<A> implements BidirectionalActions<A> {
     private List<A> fromGoalStatePartList = new ArrayList<>();
     private List<A> fromInitialStateToGoalStateList = new ArrayList<>();
     private List<A> fromGoalStateToInitialStateList = new ArrayList<>();
+    private List<A> fromMeetingStateToGoalStateList = new ArrayList<>();
+    private List<A> fromMeetingStateToInitialStateList = new ArrayList<>();
 
-    public BasicBidirectionalActions(List<A> fromInitialStatePartList, List<A> fromGoalStatePartList) {
+    public BasicBidirectionalActions(List<A> fromInitialStatePartList, List<A> fromGoalStatePartList,List<A> fromMeetingStateToInitialStateList,List<A> fromMeetingStateToGoalStateList) {
         this.fromInitialStatePartList = fromInitialStatePartList;
         this.fromGoalStatePartList = fromGoalStatePartList;
+        this.fromMeetingStateToGoalStateList = fromMeetingStateToGoalStateList;
+        this.fromMeetingStateToInitialStateList= fromMeetingStateToInitialStateList;
     }
 
     private void init() {
@@ -36,21 +42,17 @@ public List<A> fromGoalStatePart() {
 
     @Override
     public List<A> fromInitialStateToGoalState() {
-        List<A> reversedFromGoalStatePart = new ArrayList<>(fromGoalStatePart());
-        Collections.reverse(reversedFromGoalStatePart);
         init();
         fromInitialStateToGoalStateList.addAll(fromInitialStatePart());
-        fromInitialStateToGoalStateList.addAll(reversedFromGoalStatePart);
+        fromInitialStateToGoalStateList.addAll(fromMeetingStateToGoalStateList);
         return fromInitialStateToGoalStateList;
     }
 
     @Override
     public List<A> fromGoalStateToInitialState() {
-        List<A> reversedFromInitialStatePart = new ArrayList<>(fromInitialStatePart());
-        Collections.reverse(reversedFromInitialStatePart);
         init();
         fromGoalStateToInitialStateList.addAll(fromGoalStatePart());
-        fromGoalStateToInitialStateList.addAll(reversedFromInitialStatePart);
+        fromGoalStateToInitialStateList.addAll(fromMeetingStateToInitialStateList);
         return fromGoalStateToInitialStateList;
     }
 

core/src/main/java/aima/core/search/basic/uninformed/BidirectionalSearch.java

@@ -15,7 +15,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Queue;
-
+import java.util.LinkedList;
 /**
  * Artificial Intelligence A Modern Approach (4th Edition): Figure ??, page ??.
  * <br>
@@ -35,14 +35,16 @@ public class BidirectionalSearch<A, S> implements SearchForActionsBidirectionall
     private Node<A, S> meetingOfTwoFrontiers;
     private Node<A, S> nextNodeToBeEvaluated;
     private boolean fromFront;
+    private Problem<A, S> problem;
     @Override
 
     public BidirectionalActions<A> apply(Problem<A, S> originalProblem, Problem<A, S> reverseProblem) {
+        problem = originalProblem;
         Node<A, S> node = newRootNode(originalProblem.initialState(), 0);
         if (originalProblem.isGoalState(node.state())) {
             this.previousMeetingOfTwoFrontiers = node;
             this.nextNodeToBeEvaluated = null;
-            bidirectionalActions = new BasicBidirectionalActions<>(fromInitialStatePart(), fromGoalStatePart());
+            bidirectionalActions = new BasicBidirectionalActions<>(fromInitialStatePart(), fromGoalStatePart(), fromMeetingStateToInitialState(), fromMeetingStateToGoalState());
             return bidirectionalActions;
         }
         Node<A, S> revNode = newRootNode(reverseProblem.initialState(), 0);
@@ -55,16 +57,16 @@ public BidirectionalActions<A> apply(Problem<A, S> originalProblem, Problem<A, S
 
             // Existence of path is checked from both ends of the problem.
             if (isSolution(pathExistsBidirectional(front, exploredFront, exploredBack, originalProblem), true)) {
-                bidirectionalActions = new BasicBidirectionalActions<>(fromInitialStatePart(), fromGoalStatePart());
+                bidirectionalActions = new BasicBidirectionalActions<>(fromInitialStatePart(), fromGoalStatePart(), fromMeetingStateToInitialState(), fromMeetingStateToGoalState());
                 return bidirectionalActions;
             }
             if (isSolution(pathExistsBidirectional(back, exploredBack, exploredFront, reverseProblem), false)) {
-                bidirectionalActions = new BasicBidirectionalActions<>(fromInitialStatePart(), fromGoalStatePart());
+                bidirectionalActions = new BasicBidirectionalActions<>(fromInitialStatePart(), fromGoalStatePart(), fromMeetingStateToInitialState(), fromMeetingStateToGoalState());
                 return bidirectionalActions;
             }
         }
         this.previousMeetingOfTwoFrontiers = null;
-        bidirectionalActions = new BasicBidirectionalActions<>(fromInitialStatePart(), fromGoalStatePart());
+        bidirectionalActions = new BasicBidirectionalActions<>(fromInitialStatePart(), fromGoalStatePart(), fromMeetingStateToInitialState(), fromMeetingStateToGoalState());
         return bidirectionalActions;
     }
 
@@ -167,4 +169,44 @@ private List<A> fromGoalStatePart() {
             return fromGoalStatePartList;
         }
     }
+
+    private List<A> fromMeetingStateToInitialState() {
+        if (this.previousMeetingOfTwoFrontiers == null || this.nextNodeToBeEvaluated == null)
+            return failure();
+        if (!this.fromFront) {
+            return buildPath(this.nextNodeToBeEvaluated);
+        } else {
+            return buildPath(this.meetingOfTwoFrontiers);
+        }
+    }
+
+    private List<A> fromMeetingStateToGoalState() {
+        if (this.previousMeetingOfTwoFrontiers == null || this.nextNodeToBeEvaluated == null)
+            return failure();
+        if (this.fromFront) {
+            return buildPath(this.nextNodeToBeEvaluated);
+        } else {
+            return buildPath(this.meetingOfTwoFrontiers);
+        }
+    }
+
+    private List<A> buildPath(Node<A, S> node) {
+        LinkedList<A> result = new LinkedList<>();
+        result.add(node.action());
+        List<A> actions;
+        while (node.parent() != null) {
+            actions = problem.actions(node.state());
+            Node<A, S> finalNode = node;
+            double pathCost = Double.POSITIVE_INFINITY;
+            for (A action : actions) {
+                Node<A, S> child = newChildNode(problem, finalNode, action);
+                if (finalNode.parent().state().equals(child.state()) && child.pathCost() < pathCost) {
+                    result.add(action);
+                    pathCost = child.pathCost();
+                }
+            }
+            node = node.parent();
+        }
+        return result;
+    }
 }

test/src/test/java/aima/test/unit/search/support/BasicBidirectionalActionsTest.java

@@ -15,7 +15,9 @@ public class BasicBidirectionalActionsTest {
     public void testBasicBidirectionalActions() {
         List<String> fromInitialStatePartList = Arrays.asList("start", "second", "third");
         List<String> fromGoalStatePartList = Arrays.asList("goal", "fifth", "fourth");
-        BasicBidirectionalActions<String> basicBidirectionalActions = new BasicBidirectionalActions<>(fromInitialStatePartList, fromGoalStatePartList);
+        List<String> fromMeetingStateToInitialState = Arrays.asList("third", "second", "start");
+        List<String> fromMeetingStateToGoalState = Arrays.asList("fourth", "fifth", "goal");
+        BasicBidirectionalActions<String> basicBidirectionalActions = new BasicBidirectionalActions<>(fromInitialStatePartList, fromGoalStatePartList, fromMeetingStateToInitialState,fromMeetingStateToGoalState);
         Assert.assertEquals(
                 Arrays.asList("start", "second", "third", "fourth", "fifth", "goal"),
                 basicBidirectionalActions.fromInitialStateToGoalState());

test/src/test/java/aima/test/unit/search/uninformed/BidirectionalSearchTest.java

@@ -70,14 +70,16 @@ public void timisoaraToUrziceni() throws Exception {
             new GoAction(ARAD),
             new GoAction(SIBIU),
             new GoAction(FAGARAS),
-            new GoAction(BUCHAREST)),
+            new GoAction(BUCHAREST),
+            new GoAction(URZICENI)),
             solution.fromInitialStateToGoalState());
 
         assertEquals(Arrays.asList(
             new GoAction(BUCHAREST),
             new GoAction(FAGARAS),
             new GoAction(SIBIU),
-            new GoAction(ARAD)),
+            new GoAction(ARAD),
+            new GoAction(TIMISOARA)),
             solution.fromGoalStateToInitialState());
     }