Improvement of BinaryHeap.remove() with a HashMap to avoid iterating through the list

be-graphes-algos/src/main/java/org/insa/graphs/algorithm/utils/BinaryHeap.java

@@ -1,10 +1,12 @@
 package org.insa.graphs.algorithm.utils;
 
 import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.Map;
 
 /**
  * Implements a binary heap containing elements of type E.
- *
+ * <p>
  * Note that all comparisons are based on the compareTo method, hence E must
  * implement Comparable
  *
@@ -15,6 +17,7 @@ public class BinaryHeap<E extends Comparable<E>> implements PriorityQueue<E> {
 
     // Number of elements in heap.
     private int currentSize;
+    private Map<E, Integer> elementIndexes = new HashMap<>();
 
     // The heap array.
     protected final ArrayList<E> array;
@@ -35,10 +38,12 @@ public class BinaryHeap<E extends Comparable<E>> implements PriorityQueue<E> {
     public BinaryHeap(BinaryHeap<E> heap) {
         this.currentSize = heap.currentSize;
         this.array = new ArrayList<E>(heap.array);
+        this.elementIndexes = new HashMap<>(heap.elementIndexes);
     }
 
     /**
      * Check if each element is lower than its children
+     *
      * @return true if valid, false otherwise
      */
     public boolean isValid() {
@@ -67,10 +72,10 @@ public class BinaryHeap<E extends Comparable<E>> implements PriorityQueue<E> {
      * @param value Element to set.
      */
     private void arraySet(int index, E value) {
+        elementIndexes.put(value, index);
         if (index == this.array.size()) {
             this.array.add(value);
-        }
-        else {
+        } else {
             this.array.set(index, value);
         }
     }
@@ -104,9 +109,7 @@ public class BinaryHeap<E extends Comparable<E>> implements PriorityQueue<E> {
     private void percolateUp(int index) {
         E x = this.array.get(index);
 
-        for (; index > 0
-                && x.compareTo(this.array.get(indexParent(index))) < 0; index = indexParent(
-                        index)) {
+        for (; index > 0 && x.compareTo(this.array.get(indexParent(index))) < 0; index = indexParent(index)) {
             E moving_val = this.array.get(indexParent(index));
             this.arraySet(index, moving_val);
         }
@@ -136,8 +139,7 @@ public class BinaryHeap<E extends Comparable<E>> implements PriorityQueue<E> {
                     this.arraySet(ileft, current);
                     this.percolateDown(ileft);
                 }
-            }
-            else {
+            } else {
                 // Right is smaller
                 if (right.compareTo(current) < 0) {
                     this.arraySet(index, right);
@@ -167,22 +169,15 @@ public class BinaryHeap<E extends Comparable<E>> implements PriorityQueue<E> {
 
     @Override
     public void remove(E x) throws ElementNotFoundException {
-        int index = 0;
-        // We avoid array.indexOf(x) because we don't need to search
-        // through the whole list, we can stop at indexSize.
-        boolean found = false;
-        while(!found && index < currentSize) {
-            if (array.get(index) == x)
-                found =true;
-            else
-                index++;
-        }
-
-        if (!found) throw new ElementNotFoundException(x);
-        arraySet(index, array.get(--currentSize));
+        Integer index = elementIndexes.remove(x);
+        if (index == null) throw new ElementNotFoundException(x);
+        currentSize--;
+        if (currentSize != 0 && index != currentSize) {
+            arraySet(index, array.get(currentSize));
             percolateUp(index);
             percolateDown(index);
         }
+    }
 
     @Override
     public E findMin() throws EmptyPriorityQueueException {
@@ -194,9 +189,13 @@ public class BinaryHeap<E extends Comparable<E>> implements PriorityQueue<E> {
     @Override
     public E deleteMin() throws EmptyPriorityQueueException {
         E minItem = findMin();
-        E lastItem = this.array.get(--this.currentSize);
+        elementIndexes.remove(minItem);
+        currentSize--;
+        if (currentSize != 0) {
+            E lastItem = this.array.get(this.currentSize);
             this.arraySet(0, lastItem);
             this.percolateDown(0);
+        }
         return minItem;
     }
 
@@ -214,7 +213,6 @@ public class BinaryHeap<E extends Comparable<E>> implements PriorityQueue<E> {
      *
      * @param maxElement Maximum number of elements to display. or {@code -1} to
      *                   display all the elements.
-     * 
      * @return a string containing a sorted view this binary heap.
      */
     public String toStringSorted(int maxElement) {
@@ -234,7 +232,6 @@ public class BinaryHeap<E extends Comparable<E>> implements PriorityQueue<E> {
      * Creates a multi-lines string representing a tree view of this binary heap.
      *
      * @param maxDepth Maximum depth of the tree to display.
-     * 
      * @return a string containing a tree view of this binary heap.
      */
     public String toStringTree(int maxDepth) {