Initial commit.
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Mikael Capelle
252
src/main/org/insa/utility/BinaryHeap.java
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252
src/main/org/insa/utility/BinaryHeap.java
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//
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// ******************PUBLIC OPERATIONS*********************
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// void insert( x ) --> Insert x
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// Comparable deleteMin( )--> Return and remove smallest item
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// Comparable findMin( ) --> Return smallest item
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// boolean isEmpty( ) --> Return true if empty; else false
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// ******************ERRORS********************************
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// Throws RuntimeException for findMin and deleteMin when empty
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package org.insa.utility;
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import java.util.* ;
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/**
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* Implements a binary heap.
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* Note that all "matching" is based on the compareTo method.
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* @author Mark Allen Weiss
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* @author DLB
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*/
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public class BinaryHeap<E extends Comparable<E>> {
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private int currentSize; // Number of elements in heap
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// Java genericity does not work with arrays.
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// We have to use an ArrayList
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private ArrayList<E> array; // The heap array
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/**
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* Construct the binary heap.
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*/
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public BinaryHeap() {
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this.currentSize = 0;
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this.array = new ArrayList<E>() ;
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}
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// Constructor used for debug.
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public BinaryHeap(BinaryHeap<E> heap) {
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this.currentSize = heap.currentSize ;
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this.array = new ArrayList<E>(heap.array) ;
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}
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// Sets an element in the array
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private void arraySet(int index, E value) {
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if (index == this.array.size()) {
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this.array.add(value) ;
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}
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else {
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this.array.set(index, value) ;
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}
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}
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/**
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* Test if the heap is logically empty.
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* @return true if empty, false otherwise.
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*/
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public boolean isEmpty() { return this.currentSize == 0; }
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/**
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* Returns size.
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* @return current size.
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*/
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public int size() { return this.currentSize; }
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/**
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* Returns index of parent.
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*/
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private int index_parent(int index) {
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return (index - 1) / 2 ;
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}
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/**
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* Returns index of left child.
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*/
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private int index_left(int index) {
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return index * 2 + 1 ;
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}
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/**
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* Insert into the heap.
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* @param x the item to insert.
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*/
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public void insert(E x) {
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int index = this.currentSize++ ;
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this.arraySet(index, x) ;
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this.percolateUp(index) ;
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}
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/**
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* Internal method to percolate up in the heap.
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* @param index the index at which the percolate begins.
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*/
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private void percolateUp(int index) {
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E x = this.array.get(index) ;
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for( ; index > 0 && x.compareTo(this.array.get(index_parent(index)) ) < 0; index = index_parent(index) ) {
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E moving_val = this.array.get(index_parent(index)) ;
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this.arraySet(index, moving_val) ;
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}
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this.arraySet(index, x) ;
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}
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/**
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* Internal method to percolate down in the heap.
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* @param index the index at which the percolate begins.
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*/
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private void percolateDown(int index) {
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int ileft = index_left(index) ;
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int iright = ileft + 1 ;
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if (ileft < this.currentSize) {
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E current = this.array.get(index) ;
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E left = this.array.get(ileft) ;
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boolean hasRight = iright < this.currentSize ;
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E right = (hasRight)?this.array.get(iright):null ;
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if (!hasRight || left.compareTo(right) < 0) {
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// Left is smaller
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if (left.compareTo(current) < 0) {
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this.arraySet(index, left) ;
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this.arraySet(ileft, current) ;
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this.percolateDown( ileft ) ;
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}
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}
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else {
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// Right is smaller
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if (right.compareTo(current) < 0) {
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this.arraySet(index, right) ;
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this.arraySet(iright, current) ;
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this.percolateDown( iright ) ;
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}
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}
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}
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}
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/**
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* Find the smallest item in the heap.
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* @return the smallest item.
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* @throws Exception if empty.
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*/
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public E findMin( ) {
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if( isEmpty() )
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throw new RuntimeException( "Empty binary heap" );
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return this.array.get(0);
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}
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/**
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* Remove the smallest item from the heap.
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* @return the smallest item.
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* @throws Exception if empty.
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*/
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public E deleteMin( ) {
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E minItem = findMin( );
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E lastItem = this.array.get(--this.currentSize) ;
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this.arraySet(0, lastItem) ;
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this.percolateDown( 0 );
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return minItem;
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}
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/**
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* Prints the heap
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*/
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public void print() {
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System.out.println() ;
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System.out.println("======== HEAP (size = " + this.currentSize + ") ========") ;
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System.out.println() ;
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for (int i = 0 ; i < this.currentSize ; i++) {
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System.out.println(this.array.get(i).toString()) ;
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}
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System.out.println() ;
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System.out.println("-------- End of heap --------") ;
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System.out.println() ;
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}
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/**
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* Prints the elements of the heap according to their respective order.
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*/
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public void printSorted() {
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BinaryHeap<E> copy = new BinaryHeap<E>(this) ;
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System.out.println() ;
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System.out.println("======== Sorted HEAP (size = " + this.currentSize + ") ========") ;
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System.out.println() ;
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while (!copy.isEmpty()) {
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System.out.println(copy.deleteMin()) ;
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}
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System.out.println() ;
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System.out.println("-------- End of heap --------") ;
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System.out.println() ;
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}
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// Test program : compare with the reference implementation PriorityQueue.
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public static void main(String [] args) {
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BinaryHeap<Integer> heap = new BinaryHeap<Integer>() ;
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PriorityQueue<Integer> queue = new PriorityQueue<Integer>() ;
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int count = 0 ;
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int blocksize = 10000 ;
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System.out.println("Interrupt to stop the test.") ;
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while (true) {
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// Insert up to blocksize elements
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int nb_insert = (int)(Math.random() * (blocksize + 1)) ;
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for (int i = 0 ; i < nb_insert ; i++) {
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Integer obj = new Integer(i) ;
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heap.insert(obj) ;
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queue.add(obj) ;
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}
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// Remove up to blocksize elements
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int nb_remove = (int)(Math.random() * blocksize * 1.1) ;
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if (nb_remove > queue.size()) {
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nb_remove = queue.size() ;
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}
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for (int i = 0 ; i < nb_remove ; i++) {
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int removed1 = queue.poll().intValue() ;
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int removed2 = heap.deleteMin().intValue() ;
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if (removed1 != removed2) {
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System.out.println("Ouch : expected " + removed1 + " .. but got " + removed2) ;
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System.exit(1) ;
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}
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}
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if (heap.size() != queue.size()) {
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System.out.println("Ouch : heap size = " + heap.size() + " queue size = " + queue.size() ) ;
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System.exit(1) ;
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}
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count += nb_remove ;
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if (count > 1000000) {
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System.out.println("" + count + " items successfully compared. Heap size : " + heap.size()) ;
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count = 0 ;
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}
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}
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}
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}
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