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The OpenTripPlanner multimodal journey planning system
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);
}
}