83 lines
1.6 KiB
Java
83 lines
1.6 KiB
Java
|
import java.util.*;
|
||
|
|
|
||
|
|
// https://en.wikipedia.org/wiki/Binary_heap
|
||
|
|
// invariant: heap[parent] <= heap[child]
|
||
|
|
public class BinaryHeap {
|
||
|
|
int[] heap;
|
||
|
|
int size;
|
||
|
|
|
||
|
|
public BinaryHeap(int n) {
|
||
|
|
heap = new int[n];
|
||
|
|
}
|
||
|
|
|
||
|
|
// build heap in O(n)
|
||
|
|
public BinaryHeap(int[] values) {
|
||
|
|
heap = values.clone();
|
||
|
|
size = values.length;
|
||
|
|
for (int pos = size / 2 - 1; pos >= 0; pos--)
|
||
|
|
down(pos);
|
||
|
|
}
|
||
|
|
|
||
|
|
public int removeMin() {
|
||
|
|
int removed = heap[0];
|
||
|
|
heap[0] = heap[--size];
|
||
|
|
down(0);
|
||
|
|
return removed;
|
||
|
|
}
|
||
|
|
|
||
|
|
public void add(int value) {
|
||
|
|
heap[size] = value;
|
||
|
|
up(size++);
|
||
|
|
}
|
||
|
|
|
||
|
|
void up(int pos) {
|
||
|
|
while (pos > 0) {
|
||
|
|
int parent = (pos - 1) / 2;
|
||
|
|
if (heap[pos] >= heap[parent])
|
||
|
|
break;
|
||
|
|
swap(pos, parent);
|
||
|
|
pos = parent;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
void down(int pos) {
|
||
|
|
while (true) {
|
||
|
|
int child = 2 * pos + 1;
|
||
|
|
if (child >= size)
|
||
|
|
break;
|
||
|
|
if (child + 1 < size && heap[child + 1] < heap[child])
|
||
|
|
++child;
|
||
|
|
if (heap[pos] <= heap[child])
|
||
|
|
break;
|
||
|
|
swap(pos, child);
|
||
|
|
pos = child;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
void swap(int i, int j) {
|
||
|
|
int t = heap[i];
|
||
|
|
heap[i] = heap[j];
|
||
|
|
heap[j] = t;
|
||
|
|
}
|
||
|
|
|
||
|
|
// random test
|
||
|
|
public static void main(String[] args) {
|
||
|
|
Random rnd = new Random(1);
|
||
|
|
for (int step = 0; step < 1000; step++) {
|
||
|
|
int n = rnd.nextInt(100) + 1;
|
||
|
|
PriorityQueue<Integer> q = new PriorityQueue<>();
|
||
|
|
BinaryHeap h = new BinaryHeap(n);
|
||
|
|
for (int op = 0; op < 1000; op++) {
|
||
|
|
if (rnd.nextBoolean() && q.size() < n) {
|
||
|
|
int v = rnd.nextInt();
|
||
|
|
q.add(v);
|
||
|
|
h.add(v);
|
||
|
|
} else if (!q.isEmpty()) {
|
||
|
|
if (q.remove() != h.removeMin())
|
||
|
|
throw new RuntimeException();
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|