Merge pull request #156 from michaelhaaf/contrib/issue-137

close #137 to replace Stack with ArrayDeque

hipster-core/src/main/java/es/usc/citius/hipster/algorithm/DepthFirstSearch.java

@@ -19,10 +19,7 @@
 import es.usc.citius.hipster.model.Node;
 import es.usc.citius.hipster.model.function.NodeExpander;
 
-import java.util.HashSet;
-import java.util.Iterator;
-import java.util.Set;
-import java.util.Stack;
+import java.util.*;
 
 /**
  * <p>
@@ -90,13 +87,13 @@ public boolean isProcessed() {
      * DFS iterator used to expand always the deepest non-visited node.
      */
     public class Iterator implements java.util.Iterator<N> {
-        protected Stack<StackFrameNode> stack = new Stack<StackFrameNode>();
+        protected Deque<StackFrameNode> stack = new ArrayDeque<StackFrameNode>();
         protected StackFrameNode next;
         protected Set<S> closed = new HashSet<S>();
         protected boolean graphSupport = true;
 
         protected Iterator(){
-            this.stack.add(new StackFrameNode(initialNode));
+            this.stack.addLast(new StackFrameNode(initialNode));
         }
 
 
@@ -155,30 +152,30 @@ protected StackFrameNode processNextNode(){
 
             if (stack.isEmpty()) return null;
 
-            // Take current node in the stack but do not remove
-            StackFrameNode current = stack.peek();
+            // Take last node in the stack but do not remove
+            StackFrameNode current = stack.peekLast();
             // Find a successor
             if (current.successors.hasNext()){
                 N successor = current.successors.next();
                 // push the node (if not explored)
                 if (!graphSupport || !closed.contains(successor.state())) {
-                    stack.add(new StackFrameNode(successor));
+                    stack.addLast(new StackFrameNode(successor));
                 }
                 return current;
             } else {
                 // Visited?
                 if (current.visited){
                     current.processed = true;
                 }
-                return stack.pop();
+                return stack.removeFirst();
             }
         }
 
-        public Stack<StackFrameNode> getStack() {
+        public Deque<StackFrameNode> getStack() {
             return stack;
         }
 
-        public void setStack(Stack<StackFrameNode> stack) {
+        public void setStack(Deque<StackFrameNode> stack) {
             this.stack = stack;
         }
 

hipster-core/src/main/java/es/usc/citius/hipster/algorithm/IDAStar.java

@@ -22,7 +22,8 @@
 import es.usc.citius.hipster.model.HeuristicNode;
 import es.usc.citius.hipster.model.function.NodeExpander;
 
-import java.util.Stack;
+import java.util.ArrayDeque;
+import java.util.Deque;
 
 /**
  * <p>
@@ -81,7 +82,7 @@ private class StackFrameNode {
      * backtracking.
      */
     public class Iterator implements java.util.Iterator<N> {
-        protected Stack<StackFrameNode> stack = new Stack<StackFrameNode>();
+        protected Deque<StackFrameNode> stack = new ArrayDeque<>();
         protected C fLimit;
         protected C minfLimit;
         protected int reinitialization = 0;
@@ -91,7 +92,7 @@ protected Iterator(){
             // Set initial bound
             fLimit = initialNode.getEstimation();
             minfLimit = null;
-            this.stack.add(new StackFrameNode(initialNode));
+            this.stack.addLast(new StackFrameNode(initialNode));
         }
 
         @Override
@@ -148,7 +149,7 @@ protected StackFrameNode nextUnvisited(){
                         fLimit = minfLimit;
                         reinitialization++;
                         minfLimit = null;
-                        stack.add(new StackFrameNode(initialNode));
+                        stack.addLast(new StackFrameNode(initialNode));
                         nextNode = processNextNode();
                     }
                 }
@@ -174,8 +175,8 @@ protected StackFrameNode processNextNode(){
             // 1- If the stack is empty, change fLimit and reinitialize the search
             if (stack.isEmpty()) return null;
 
-            // Take current node in the stack but do not remove
-            StackFrameNode current = stack.peek();
+            // Take last node in the stack but do not remove
+            StackFrameNode current = stack.peekLast();
 
             // 2 - Check if the current node exceeds the limit bound
             C fCurrent = current.node.getScore();
@@ -184,31 +185,31 @@ protected StackFrameNode processNextNode(){
                 updateMinFLimit(fCurrent);
                 // Remove from stack
                 current.processed = true;
-                return stack.pop();
+                return stack.removeLast();
             }
 
             // Find a successor
             if (current.successors.hasNext()){
                 // 3 - Node has at least one neighbor
                 N successor = current.successors.next();
                 // push the node
-                stack.add(new StackFrameNode(successor));
+                stack.addLast(new StackFrameNode(successor));
                 return current;
 
             } else {
                 // 4 - Visited?
                 if (current.visited){
                     current.processed = true;
                 }
-                return stack.pop();
+                return stack.removeLast();
             }
         }
 
-        public Stack<StackFrameNode> getStack() {
+        public Deque<StackFrameNode> getStack() {
             return stack;
         }
 
-        public void setStack(Stack<StackFrameNode> stack) {
+        public void setStack(Deque<StackFrameNode> stack) {
             this.stack = stack;
         }
 

hipster-core/src/main/java/es/usc/citius/hipster/algorithm/MultiobjectiveLS.java

@@ -56,7 +56,7 @@ public MultiobjectiveLS(N initialNode, NodeExpander<A, S, N> nodeExpander) {
     public class Iterator implements java.util.Iterator<N> {
         protected Queue<N> queue = new LinkedList<N>();
         public Map<S, Collection<N>> nonDominated;
-        //auxiliar variable which stores an empty list to avoid nullable values in code
+        //auxiliary variable which stores an empty list to avoid nullable values in code
         private final Collection<N> EMPTYLIST = new ArrayList<N>();
 
         protected Iterator(){