org.jheaps.tree.SkewHeap Maven / Gradle / Ivy
/*
* (C) Copyright 2014-2016, by Dimitrios Michail
*
* JHeaps Library
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.jheaps.tree;
import java.io.Serializable;
import java.util.Comparator;
import java.util.NoSuchElementException;
import org.jheaps.AddressableHeap;
import org.jheaps.MergeableAddressableHeap;
import org.jheaps.annotations.ConstantTime;
import org.jheaps.annotations.LogarithmicTime;
/**
* Skew heaps. The heap is sorted according to the {@linkplain Comparable
* natural ordering} of its keys, or by a {@link Comparator} provided at heap
* creation time, depending on which constructor is used.
*
*
* Operations {@code insert}, {@code deleteMin}, and {@code delete} take
* amortized O(log(n)). Operation {@code findMin} is worst-case O(1). Note that
* a skew-heap does not efficiently support the operation {@code decreaseKey}
* which is amortized Ω(log(n)).
*
*
* Note that the ordering maintained by this heap, like any heap, and whether or
* not an explicit comparator is provided, must be consistent with
* {@code equals} if this heap is to correctly implement the {@code Heap}
* interface. (See {@code Comparable} or {@code Comparator} for a precise
* definition of consistent with equals.) This is so because the
* {@code Heap} interface is defined in terms of the {@code equals} operation,
* but this heap performs all key comparisons using its {@code compareTo} (or
* {@code compare}) method, so two keys that are deemed equal by this method
* are, from the standpoint of this heap, equal. The behavior of a heap
* is well-defined even if its ordering is inconsistent with
* {@code equals}; it just fails to obey the general contract of the
* {@code Heap} interface.
*
*
* Note that this implementation is not synchronized. If
* multiple threads access a heap concurrently, and at least one of the threads
* modifies the heap structurally, it must be synchronized externally.
* (A structural modification is any operation that adds or deletes one or more
* elements or changing the key of some element.) This is typically accomplished
* by synchronizing on some object that naturally encapsulates the heap.
*
* @param
* the type of keys maintained by this heap
* @param
* the type of values maintained by this heap
*
* @author Dimitrios Michail
*/
public class SkewHeap implements MergeableAddressableHeap, Serializable {
private final static long serialVersionUID = 1;
/**
* The comparator used to maintain order in this heap, or null if it uses
* the natural ordering of its keys.
*
* @serial
*/
protected final Comparator comparator;
/**
* Size of the heap
*/
protected long size;
/**
* Root node of the heap
*/
protected Node root;
/**
* Used to reference the current heap or some other heap in case of melding,
* so that handles remain valid even after a meld, without having to iterate
* over them.
*
* In order to avoid maintaining a full-fledged union-find data structure,
* we disallow a heap to be used in melding more than once. We use however,
* path-compression in case of cascading melds, that it, a handle moves from
* one heap to another and then another.
*/
protected SkewHeap other;
/**
* Constructs a new, empty heap, using the natural ordering of its keys.
*
*
* All keys inserted into the heap must implement the {@link Comparable}
* interface. Furthermore, all such keys must be mutually
* comparable: {@code k1.compareTo(k2)} must not throw a
* {@code ClassCastException} for any keys {@code k1} and {@code k2} in the
* heap. If the user attempts to put a key into the heap that violates this
* constraint (for example, the user attempts to put a string key into a
* heap whose keys are integers), the {@code insert(Object key)} call will
* throw a {@code ClassCastException}.
*/
public SkewHeap() {
this(null);
}
/**
* Constructs a new, empty heap, ordered according to the given comparator.
*
*
* All keys inserted into the heap must be mutually comparable by
* the given comparator: {@code comparator.compare(k1,
* k2)} must not throw a {@code ClassCastException} for any keys {@code k1}
* and {@code k2} in the heap. If the user attempts to put a key into the
* heap that violates this constraint, the {@code insert(Object key)} call
* will throw a {@code ClassCastException}.
*
* @param comparator
* the comparator that will be used to order this heap. If
* {@code null}, the {@linkplain Comparable natural ordering} of
* the keys will be used.
*/
public SkewHeap(Comparator comparator) {
this.comparator = comparator;
this.size = 0;
this.root = null;
this.other = this;
}
/**
* {@inheritDoc}
*/
@Override
@LogarithmicTime(amortized = true)
public AddressableHeap.Handle insert(K key) {
return insert(key, null);
}
/**
* {@inheritDoc}
*/
@Override
@LogarithmicTime(amortized = true)
@SuppressWarnings("unchecked")
public AddressableHeap.Handle insert(K key, V value) {
if (other != this) {
throw new IllegalStateException("A heap cannot be used after a meld");
}
if (key == null) {
throw new NullPointerException("Null keys not permitted");
}
Node n = createNode(key, value);
// easy special cases
if (size == 0) {
root = n;
size = 1;
return n;
} else if (size == 1) {
int c;
if (comparator == null) {
c = ((Comparable) key).compareTo(root.key);
} else {
c = comparator.compare(key, root.key);
}
if (c <= 0) {
n.o_c = root;
root.y_s = n;
root = n;
} else {
root.o_c = n;
n.y_s = root;
}
size = 2;
return n;
}
if (comparator == null) {
root = union(root, n);
} else {
root = unionWithComparator(root, n);
}
size++;
return n;
}
/**
* {@inheritDoc}
*/
@Override
@ConstantTime
public AddressableHeap.Handle findMin() {
if (size == 0) {
throw new NoSuchElementException();
}
return root;
}
/**
* {@inheritDoc}
*/
@Override
@LogarithmicTime(amortized = true)
public Handle deleteMin() {
if (size == 0) {
throw new NoSuchElementException();
}
Node oldRoot = root;
// easy special cases
if (size == 1) {
root = null;
size = 0;
return oldRoot;
} else if (size == 2) {
root = root.o_c;
root.o_c = null;
root.y_s = null;
size = 1;
oldRoot.o_c = null;
return oldRoot;
}
root = unlinkAndUnionChildren(root);
size--;
return oldRoot;
}
/**
* {@inheritDoc}
*/
@Override
@ConstantTime
public boolean isEmpty() {
return size == 0;
}
/**
* {@inheritDoc}
*/
@Override
@ConstantTime
public long size() {
return size;
}
/**
* {@inheritDoc}
*/
@Override
public Comparator comparator() {
return comparator;
}
/**
* {@inheritDoc}
*/
@Override
@ConstantTime
public void clear() {
root = null;
size = 0;
}
@Override
public void meld(MergeableAddressableHeap other) {
SkewHeap h = (SkewHeap) other;
// check same comparator
if (comparator != null) {
if (h.comparator == null || !h.comparator.equals(comparator)) {
throw new IllegalArgumentException("Cannot meld heaps using different comparators!");
}
} else if (h.comparator != null) {
throw new IllegalArgumentException("Cannot meld heaps using different comparators!");
}
if (h.other != h) {
throw new IllegalStateException("A heap cannot be used after a meld.");
}
// perform the meld
size += h.size;
if (comparator == null) {
root = union(root, h.root);
} else {
root = unionWithComparator(root, h.root);
}
// clear other
h.size = 0;
h.root = null;
// take ownership
h.other = this;
}
// ~-----------------------------------------------------------------------------
static class Node implements AddressableHeap.Handle, Serializable {
private final static long serialVersionUID = 1;
/*
* We maintain explicitly the belonging heap, instead of using an inner
* class due to possible cascading melding.
*/
SkewHeap heap;
K key;
V value;
Node o_c; // older child
Node y_s; // younger sibling or parent
Node(SkewHeap heap, K key, V value) {
this.heap = heap;
this.key = key;
this.value = value;
this.o_c = null;
this.y_s = null;
}
@Override
public K getKey() {
return key;
}
@Override
public V getValue() {
return value;
}
@Override
public void setValue(V value) {
this.value = value;
}
@Override
public void decreaseKey(K newKey) {
getOwner().decreaseKey(this, newKey);
}
@Override
public void delete() {
getOwner().delete(this);
}
/*
* Get the owner heap of the handle. This is union-find with
* path-compression between heaps.
*/
SkewHeap getOwner() {
if (heap.other != heap) {
// find root
SkewHeap root = heap;
while (root != root.other) {
root = root.other;
}
// path-compression
SkewHeap cur = heap;
while (cur.other != root) {
SkewHeap next = cur.other;
cur.other = root;
cur = next;
}
heap = root;
}
return heap;
}
}
@SuppressWarnings("unchecked")
private void decreaseKey(Node n, K newKey) {
int c;
if (comparator == null) {
c = ((Comparable) newKey).compareTo(n.key);
} else {
c = comparator.compare(newKey, n.key);
}
if (c > 0) {
throw new IllegalArgumentException("Keys can only be decreased!");
}
if (c == 0 || root == n) {
n.key = newKey;
return;
}
/*
* Delete and reinsert
*/
delete(n);
n.key = newKey;
if (comparator == null) {
root = union(root, n);
} else {
root = unionWithComparator(root, n);
}
size++;
}
/**
* Create a new node.
*
* @param key
* the key
* @param value
* the value
* @return the newly created node
*/
protected Node createNode(K key, V value) {
return new Node(this, key, value);
}
/**
* Delete a node from the heap.
*
* @param n
* the node
*/
protected void delete(Node n) {
if (n == root) {
deleteMin();
return;
}
if (n.y_s == null) {
throw new IllegalArgumentException("Invalid handle!");
}
// disconnect and union children of node
Node childTree = unlinkAndUnionChildren(n);
// find parent
Node p = getParent(n);
// link children tree in place of node
if (childTree == null) {
// no children, just unlink from parent
if (p.o_c == n) {
if (n.y_s == p) {
p.o_c = null;
} else {
p.o_c = n.y_s;
}
} else {
p.o_c.y_s = p;
}
} else {
// link children tree to parent
if (p.o_c == n) {
childTree.y_s = n.y_s;
p.o_c = childTree;
} else {
p.o_c.y_s = childTree;
childTree.y_s = p;
}
}
size--;
n.o_c = null;
n.y_s = null;
}
/**
* Unlink the two children of a node and union them forming a new tree.
*
* @param n
* the node
* @return the tree which is formed by the two children subtrees of the node
*/
protected Node unlinkAndUnionChildren(Node n) {
// disconnect children
Node child1 = n.o_c;
if (child1 == null) {
return null;
}
n.o_c = null;
Node child2 = child1.y_s;
if (child2 == n) {
child2 = null;
} else {
child2.y_s = null;
}
child1.y_s = null;
if (comparator == null) {
return union(child1, child2);
} else {
return unionWithComparator(child1, child2);
}
}
/**
* Get the parent node of a given node.
*
* @param n
* the node
* @return the parent of a node
*/
protected Node getParent(Node n) {
if (n.y_s == null) {
return null;
}
Node c = n.y_s;
if (c.o_c == n) {
return c;
}
Node p1 = c.y_s;
if (p1 != null && p1.o_c == n) {
return p1;
}
return c;
}
/**
* Unlink the right child of a node.
*
* @param n
* the node
* @return the right child after unlinking
*/
protected Node unlinkRightChild(Node n) {
Node left = n.o_c;
if (left == null || left.y_s == n) {
return null;
}
Node right = left.y_s;
left.y_s = n;
right.y_s = null;
return right;
}
/**
* Top-down union of two skew heaps.
*
* @param root1
* the root of the first heap
* @param root2
* the root of the right heap
* @return the new root of the merged heap
*/
@SuppressWarnings("unchecked")
protected Node union(Node root1, Node root2) {
if (root1 == null) {
return root2;
} else if (root2 == null) {
return root1;
}
Node newRoot;
Node cur;
// find initial
int c = ((Comparable) root1.key).compareTo(root2.key);
if (c <= 0) {
newRoot = root1;
root1 = unlinkRightChild(root1);
} else {
newRoot = root2;
root2 = unlinkRightChild(root2);
}
cur = newRoot;
// merge
while (root1 != null && root2 != null) {
c = ((Comparable) root1.key).compareTo(root2.key);
if (c <= 0) {
// link as left child of cur
if (cur.o_c == null) {
root1.y_s = cur;
} else {
root1.y_s = cur.o_c;
}
cur.o_c = root1;
cur = root1;
root1 = unlinkRightChild(root1);
} else {
// link as left child of cur
if (cur.o_c == null) {
root2.y_s = cur;
} else {
root2.y_s = cur.o_c;
}
cur.o_c = root2;
cur = root2;
root2 = unlinkRightChild(root2);
}
}
while (root1 != null) {
// link as left child of cur
if (cur.o_c == null) {
root1.y_s = cur;
} else {
root1.y_s = cur.o_c;
}
cur.o_c = root1;
cur = root1;
root1 = unlinkRightChild(root1);
}
while (root2 != null) {
// link as left child of cur
if (cur.o_c == null) {
root2.y_s = cur;
} else {
root2.y_s = cur.o_c;
}
cur.o_c = root2;
cur = root2;
root2 = unlinkRightChild(root2);
}
return newRoot;
}
/**
* Top-down union of two skew heaps with comparator.
*
* @param root1
* the root of the first heap
* @param root2
* the root of the right heap
* @return the new root of the merged heap
*/
protected Node unionWithComparator(Node root1, Node root2) {
if (root1 == null) {
return root2;
} else if (root2 == null) {
return root1;
}
Node newRoot;
Node cur;
// find initial
int c = comparator.compare(root1.key, root2.key);
if (c <= 0) {
newRoot = root1;
root1 = unlinkRightChild(root1);
} else {
newRoot = root2;
root2 = unlinkRightChild(root2);
}
cur = newRoot;
// merge
while (root1 != null && root2 != null) {
c = comparator.compare(root1.key, root2.key);
if (c <= 0) {
// link as left child of cur
if (cur.o_c == null) {
root1.y_s = cur;
} else {
root1.y_s = cur.o_c;
}
cur.o_c = root1;
cur = root1;
root1 = unlinkRightChild(root1);
} else {
// link as left child of cur
if (cur.o_c == null) {
root2.y_s = cur;
} else {
root2.y_s = cur.o_c;
}
cur.o_c = root2;
cur = root2;
root2 = unlinkRightChild(root2);
}
}
while (root1 != null) {
// link as left child of cur
if (cur.o_c == null) {
root1.y_s = cur;
} else {
root1.y_s = cur.o_c;
}
cur.o_c = root1;
cur = root1;
root1 = unlinkRightChild(root1);
}
while (root2 != null) {
// link as left child of cur
if (cur.o_c == null) {
root2.y_s = cur;
} else {
root2.y_s = cur.o_c;
}
cur.o_c = root2;
cur = root2;
root2 = unlinkRightChild(root2);
}
return newRoot;
}
}