BE-Graph/src/main/org/insa/utility/BinaryHeap.java
2018-01-29 12:35:24 +01:00

252 lines
6 KiB
Java

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