org.opentripplanner.common.pqueue.BinHeap Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of otp Show documentation
Show all versions of otp Show documentation
The OpenTripPlanner multimodal journey planning system
/* This program is free software: you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public License
as published by the Free Software Foundation, either version 3 of
the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see . */
package org.opentripplanner.common.pqueue;
import java.util.Arrays;
public class BinHeap {
private static final double GROW_FACTOR = 2.0;
private double[] prio;
private T[] elem;
private int size;
private int capacity;
public BinHeap() {
this(1000);
}
@SuppressWarnings("unchecked")
public BinHeap(int capacity) {
if (capacity < 10) capacity = 10;
this.capacity = capacity;
elem = (T[]) new Object[capacity + 1]; // erasure voodoo
prio = new double[capacity + 1]; // 1-based indexing
size = 0;
prio[0] = Double.NEGATIVE_INFINITY; // set sentinel
}
public int size() {
return size;
}
public boolean empty() {
return size <= 0;
}
public double peek_min_key() {
if (size > 0)
return prio[1];
else
throw new IllegalStateException("An empty queue does not have a minimum key.");
}
public T peek_min() {
if (size > 0)
return elem[1];
else
return null;
}
public void insert_or_dec_key(T e, double p) {
throw new UnsupportedOperationException("BinHeap has no decrease key operation.");
}
public void rekey(T e, double p) {
// Perform "inefficient" but straightforward linear search
// for an element then change its key by sifting up or down
int i = 0;
for (T t : elem) {
if (t == e)
break;
i++;
}
if (i > size) {
//System.out.printf("did not find element %s\n", e);
return;
}
//System.out.printf("found element %s with key %f at %d\n", e, prio[i], i);
if (p > prio[i]) {
// sift up (as in extract)
while (i*2 <= size) {
int child = i * 2;
if (child != size && prio[child+1] < prio[child])
child ++;
if (p > prio[child]) {
elem[i] = elem[child];
prio[i] = prio[child];
i = child;
} else break;
}
elem[i] = e;
prio[i] = p;
} else {
// sift down (as in insert)
while (prio[i/2] > p) {
elem[i] = elem[i/2];
prio[i] = prio[i/2];
i /= 2;
}
elem[i] = e;
prio[i] = p;
}
}
public void dump() {
for (int i=0; i<=capacity; i++) {
String topMarker = (i > size) ? "(UNUSED)" : "";
System.out.printf("%d\t%f\t%s\t%s\n", i, prio[i], elem[i], topMarker);
}
System.out.printf("-----------------------\n");
}
public void reset() {
// empties the queue in one operation
size=0;
}
public void insert(T e, double p) {
int i;
size += 1;
if (size > capacity)
resize((int) (capacity * GROW_FACTOR));
for (i = size; prio[i/2] > p; i /= 2) {
elem[i] = elem[i/2];
prio[i] = prio[i/2];
}
elem[i] = e;
prio[i] = p;
}
public T extract_min() {
int i, child;
T minElem = elem[1];
T lastElem = elem[size];
double lastPrio = prio[size];
if (size <= 0)
return null;
size -= 1;
for (i=1; i*2 <= size; i=child) {
child = i*2;
if (child != size && prio[child+1] < prio[child])
child++;
if (lastPrio > prio[child]) {
elem[i] = elem[child];
prio[i] = prio[child];
} else break;
}
elem[i] = lastElem;
prio[i] = lastPrio;
return minElem;
}
public void resize(int capacity) {
// System.out.println("Growing queue to " + capacity);
if (capacity < size)
throw new IllegalStateException("BinHeap contains too many elements to fit in new capacity.");
this.capacity = capacity;
prio = Arrays.copyOf(prio, capacity + 1);
elem = Arrays.copyOf(elem, capacity + 1);
}
}