Merge pull request #166 from PaulJackson123/contrib/165

Contrib/165

hipster-examples/src/main/java/es/usc/citius/hipster/examples/MazeShortestPathExample.java

@@ -20,6 +20,7 @@
 import es.usc.citius.hipster.algorithm.Hipster;
 import es.usc.citius.hipster.model.Transition;
 import es.usc.citius.hipster.model.function.CostFunction;
+import es.usc.citius.hipster.model.function.HeuristicFunction;
 import es.usc.citius.hipster.model.function.impl.StateTransitionFunction;
 import es.usc.citius.hipster.model.problem.ProblemBuilder;
 import es.usc.citius.hipster.model.problem.SearchProblem;
@@ -60,8 +61,8 @@ public static void main(String[] args) throws InterruptedException {
         final Maze2D maze = example.getMaze();
         // In order to search, we need at least the origin and the goal destination.
         // We can take these two points from the default maze:
-        Point origin = maze.getInitialLoc();
-        Point goal = maze.getGoalLoc();
+        final Point origin = maze.getInitialLoc();
+        final Point goal = maze.getGoalLoc();
         // The maze is a 2D map, where each tile defined by 2D coordinates x and y
         // can be empty or occupied by an obstacle. We have to define de transition
         // function that tells the algorithm which are the available movements from
@@ -99,6 +100,16 @@ public Double evaluate(Transition<Void, Point> transition) {
                         return source.distance(destination);
                     }
                 })
+                .useHeuristicFunction(new HeuristicFunction<Point, Double>() {
+                    // Give A* an estimate for the remaining distance to goal. Estimate need not be exact as long as
+                    // it doesn't overestimate the remaining distance.
+                    @Override
+                    public Double estimate(Point state) {
+                        // Provide Euclidean distance as simple estimate.
+                        // Manhattan distance is not applicable as it doesn't support diagonal transitions.
+                        return state.distance(goal);
+                    }                    
+                })
                 .build();
 
         //MazeSearch.printSearch(Hipster.createAStar(p).iterator(), maze);