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/*
* (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.ArrayDeque;
import java.util.Comparator;
import java.util.Deque;
import java.util.NoSuchElementException;
import org.jheaps.Heap;
import org.jheaps.MergeableHeap;
import org.jheaps.annotations.ConstantTime;
import org.jheaps.annotations.VisibleForTesting;
/**
* A binary tree soft heap. 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.
*
*
* If n elements are inserted into a soft heap, then up to εn of the
* elements still contained in the heap, for a given error parameter ε, may
* be corrupted, i.e., have their keys artificially increased. In exchange for
* allowing these corruptions, each soft heap operation is performed in O(log
* 1/ε) amortized time. Note that n here is the number of elements inserted
* into the heaps, not the current number of elements in the heap which may be
* considerably smaller. Moreover the user has no control on which elements may
* be corrupted.
*
*
* This variant of the soft heap is due to Kaplan and Zwick, described in detail
* in the following
* paper:
*
* - Haim Kaplan and Uri Zwick, A simpler implementation and analysis of
* Chazelle's Soft Heaps, In Proceedings of the 20th Annual ACM-SIAM Symposium
* on Discrete Algorithms (SODA 2009), 477--485, 2009.
*
*
*
* Note that the ordering maintained by a soft 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 a pairing 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 the 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
*
* @author Dimitrios Michail
*/
public class BinaryTreeSoftHeap implements Heap, MergeableHeap, 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
*/
private final Comparator comparator;
/**
* Already computed values for target sizes.
*/
private final static long[] TARGET_SIZE = { 1, 2, 3, 5, 8, 12, 18, 27, 41, 62, 93, 140, 210, 315, 473, 710, 1065,
1598, 2397, 3596, 5394, 8091, 12137, 18206, 27309, 40964, 61446, 92169, 138254, 207381, 311072, 466608,
699912, 1049868, 1574802, 2362203, 3543305, 5314958, 7972437, 11958656, 17937984, 26906976, 40360464,
60540696, 90811044, 136216566, 204324849, 306487274, 459730911, 689596367, 1034394551, 1551591827,
2327387741L, 3491081612L, 5236622418L, 7854933627L, 11782400441L, 17673600662L, 26510400993L, 39765601490L,
59648402235L, 89472603353L, 134208905030L };
/**
* Tree nodes with less or equal than this rank will have no corrupted keys.
*/
private final int rankLimit;
/**
* The root list, in non-decreasing rank order.
*/
@VisibleForTesting
final RootList rootList;
/**
* Size of the heap.
*/
private long size;
/**
* 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}.
*
* @param errorRate
* the error rate
* @throws IllegalArgumentException
* if the error rate is less or equal to zero
* @throws IllegalArgumentException
* if the error rate is greater or equal to one
*/
public BinaryTreeSoftHeap(double errorRate) {
this(errorRate, 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 errorRate
* the error rate
* @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.
* @throws IllegalArgumentException
* if the error rate is less or equal to zero
* @throws IllegalArgumentException
* if the error rate is greater or equal to one
*/
public BinaryTreeSoftHeap(double errorRate, Comparator comparator) {
if (Double.compare(errorRate, 0d) <= 0) {
throw new IllegalArgumentException("Error rate must be positive");
}
if (Double.compare(errorRate, 1d) >= 0) {
throw new IllegalArgumentException("Error rate must be less than one");
}
this.rankLimit = (int) Math.ceil(Math.log(1d / errorRate) / Math.log(2d)) + 5;
this.rootList = new RootList();
this.comparator = comparator;
this.size = 0;
}
/**
* {@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() {
rootList.head = null;
rootList.tail = null;
size = 0;
}
/**
* {@inheritDoc}
*
* @throws IllegalArgumentException
* if {@code other} has a different error rate
*/
@Override
public void meld(MergeableHeap other) {
BinaryTreeSoftHeap h = (BinaryTreeSoftHeap) 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 (rankLimit != h.rankLimit) {
throw new IllegalArgumentException("Cannot meld heaps with different error rates!");
}
// perform the meld
mergeInto(h.rootList.head, h.rootList.tail);
size += h.size;
// clear other
h.size = 0;
h.rootList.head = null;
h.rootList.tail = null;
}
/**
* {@inheritDoc}
*/
@Override
public void insert(K key) {
/*
* Create a single element heap
*/
SoftHandle n = new SoftHandle(key);
TreeNode treeNode = new TreeNode(n);
RootListNode rootListNode = new RootListNode(treeNode);
/*
* Merge new list into old list
*/
mergeInto(rootListNode, rootListNode);
size++;
}
/**
* {@inheritDoc}
*/
@Override
public K findMin() {
if (size == 0) {
throw new NoSuchElementException();
}
return rootList.head.suffixMin.root.cHead.key;
}
/**
* {@inheritDoc}
*/
@Override
public K deleteMin() {
if (size == 0) {
throw new NoSuchElementException();
}
// find tree with minimum
RootListNode minRootListNode = rootList.head.suffixMin;
TreeNode root = minRootListNode.root;
// remove from list
SoftHandle result = root.cHead;
root.cHead = result.next;
root.cSize--;
// replenish keys if needed
if (root.cSize <= targetSize(root.rank) / 2) {
if (root.left != null || root.right != null) {
// get keys from children
sift(root);
updateSuffixMin(minRootListNode);
} else if (root.cSize == 0) {
// no children and empty list, just remove the tree
RootListNode minRootPrevListNode = minRootListNode.prev;
if (minRootPrevListNode != null) {
minRootPrevListNode.next = minRootListNode.next;
} else {
rootList.head = minRootListNode.next;
}
if (minRootListNode.next != null) {
minRootListNode.next.prev = minRootPrevListNode;
} else {
rootList.tail = minRootPrevListNode;
}
minRootListNode.prev = null;
minRootListNode.next = null;
updateSuffixMin(minRootPrevListNode);
}
}
result.next = null;
size--;
return result.key;
}
// --------------------------------------------------------------------
@VisibleForTesting
static class RootList implements Serializable {
private final static long serialVersionUID = 1;
RootListNode head;
RootListNode tail;
RootList() {
this.head = null;
this.tail = null;
}
}
// --------------------------------------------------------------------
@VisibleForTesting
static class RootListNode implements Serializable {
private final static long serialVersionUID = 1;
RootListNode next;
RootListNode prev;
RootListNode suffixMin;
TreeNode root;
RootListNode(TreeNode tree) {
this.root = tree;
this.suffixMin = this;
this.next = null;
this.prev = null;
}
}
// --------------------------------------------------------------------
@VisibleForTesting
static class TreeNode implements Serializable {
private final static long serialVersionUID = 1;
int rank;
// left child
TreeNode left;
// right child
TreeNode right;
// corrupted list head
SoftHandle cHead;
// corrupted list tail
SoftHandle cTail;
// corrupted list size
long cSize;
// corrupted key
K cKey;
TreeNode() {
this(null);
}
TreeNode(SoftHandle n) {
this.rank = 0;
this.left = null;
this.right = null;
this.cHead = n;
this.cTail = n;
if (n != null) {
this.cSize = 1;
this.cKey = n.key;
} else {
this.cSize = 0;
this.cKey = null;
}
}
}
// --------------------------------------------------------------------
@VisibleForTesting
static class SoftHandle implements Serializable {
private final static long serialVersionUID = 1;
K key;
SoftHandle next;
SoftHandle(K key) {
this.key = key;
this.next = null;
}
}
/**
* Compute the target size for a particular rank.
*
* @param rank
* the rank
* @return the target size
*/
private long targetSize(int rank) {
return rank <= rankLimit ? 1 : TARGET_SIZE[rank - rankLimit];
}
/**
* Sift elements from children nodes until the current node has enough
* elements in its list.
*
* @param x
* the node
*/
@SuppressWarnings("unchecked")
private void sift(TreeNode x) {
Deque> stack = new ArrayDeque>();
stack.push(x);
while (!stack.isEmpty()) {
x = stack.peek();
TreeNode xLeft = x.left;
TreeNode xRight = x.right;
// if leaf or list has enough elements, skip
if (xLeft == null && xRight == null || x.cSize >= targetSize(x.rank)) {
stack.pop();
continue;
}
// swap if needed
if (xLeft == null || xRight != null
&& ((comparator == null && ((Comparable) xLeft.cKey).compareTo(xRight.cKey) > 0)
|| (comparator != null && comparator.compare(xLeft.cKey, xRight.cKey) > 0))) {
x.left = xRight;
x.right = xLeft;
xLeft = x.left;
xRight = x.right;
}
// grab non-empty list from left child
xLeft.cTail.next = x.cHead;
x.cHead = xLeft.cHead;
if (x.cTail == null) {
x.cTail = xLeft.cTail;
}
x.cSize += xLeft.cSize;
// set new corrupted key
x.cKey = xLeft.cKey;
// clear left child list
xLeft.cKey = null;
xLeft.cHead = null;
xLeft.cTail = null;
xLeft.cSize = 0;
// recursively to left child if not a leaf
if (xLeft.left != null || xLeft.right != null) {
stack.push(xLeft);
} else {
x.left = null;
}
}
}
/**
* Combine two trees into a new tree.
*
* @param x
* the first tree
* @param y
* the second tree
* @return the combined tree
*/
private TreeNode combine(TreeNode x, TreeNode y) {
TreeNode z = new TreeNode();
z.left = x;
z.right = y;
z.rank = x.rank + 1;
sift(z);
return z;
}
/**
* Update all suffix minimum pointers for a node and all its predecessors in
* the root list.
*
* @param t
* the node
*/
@SuppressWarnings("unchecked")
private void updateSuffixMin(RootListNode t) {
if (comparator == null) {
while (t != null) {
if (t.next == null) {
t.suffixMin = t;
} else {
RootListNode nextSuffixMin = t.next.suffixMin;
if (((Comparable) t.root.cKey).compareTo(nextSuffixMin.root.cKey) <= 0) {
t.suffixMin = t;
} else {
t.suffixMin = nextSuffixMin;
}
}
t = t.prev;
}
} else {
while (t != null) {
if (t.next == null) {
t.suffixMin = t;
} else {
RootListNode nextSuffixMin = t.next.suffixMin;
if (comparator.compare(t.root.cKey, nextSuffixMin.root.cKey) <= 0) {
t.suffixMin = t;
} else {
t.suffixMin = nextSuffixMin;
}
}
t = t.prev;
}
}
}
/**
* Merge a list into the root list. Assumes that the two lists are sorted in
* non-decreasing order of rank.
*
* @param head
* the list head
* @param tail
* the list tail
*/
private void mergeInto(RootListNode head, RootListNode tail) {
// if root list empty, just copy
if (rootList.head == null) {
rootList.head = head;
rootList.tail = tail;
return;
}
// initialize
RootListNode resultHead;
RootListNode resultTail;
RootListNode resultTailPrev = null;
RootListNode cur1 = rootList.head;
RootListNode cur2 = head;
// add first node
if (cur1.root.rank <= cur2.root.rank) {
resultHead = cur1;
resultTail = cur1;
RootListNode cur1next = cur1.next;
cur1.next = null;
cur1 = cur1next;
if (cur1next != null) {
cur1next.prev = null;
}
} else {
resultHead = cur2;
resultTail = cur2;
RootListNode cur2next = cur2.next;
cur2.next = null;
cur2 = cur2next;
if (cur2next != null) {
cur2next.prev = null;
}
}
// merge
int rank1, rank2;
while (true) {
int resultRank = resultTail.root.rank;
// read rank1
if (cur1 != null) {
rank1 = cur1.root.rank;
} else {
if (cur2 != null && cur2.root.rank <= resultRank) {
rank1 = Integer.MAX_VALUE;
} else {
break;
}
}
// read rank2
if (cur2 != null) {
rank2 = cur2.root.rank;
} else {
if (cur1 != null && cur1.root.rank <= resultRank) {
rank2 = Integer.MAX_VALUE;
} else {
break;
}
}
if (rank1 <= rank2) {
switch (Integer.compare(rank1, resultRank)) {
case 0:
// combine into result
resultTail.root = combine(cur1.root, resultTail.root);
// remove cur1
RootListNode cur1next = cur1.next;
cur1.next = null;
if (cur1next != null) {
cur1next.prev = null;
}
cur1 = cur1next;
break;
case -1:
// can happen if three same ranks
cur1next = cur1.next;
// add before tail into result
cur1.next = resultTail;
resultTail.prev = cur1;
cur1.prev = resultTailPrev;
if (resultTailPrev != null) {
resultTailPrev.next = cur1;
} else {
resultHead = cur1;
}
resultTailPrev = cur1;
// advance cur1
if (cur1next != null) {
cur1next.prev = null;
}
cur1 = cur1next;
break;
case 1:
// append into result
resultTail.next = cur1;
cur1.prev = resultTail;
resultTailPrev = resultTail;
resultTail = cur1;
// remove cur1
cur1 = cur1.next;
resultTail.next = null;
if (cur1 != null) {
cur1.prev = null;
}
break;
}
} else {
// symmetric case rank2 < rank1
switch (Integer.compare(rank2, resultRank)) {
case 0:
// combine into result
resultTail.root = combine(cur2.root, resultTail.root);
// remove cur2
RootListNode cur2next = cur2.next;
cur2.next = null;
if (cur2next != null) {
cur2next.prev = null;
}
cur2 = cur2next;
break;
case -1:
// can happen if three same ranks
cur2next = cur2.next;
// add before tail into result
cur2.next = resultTail;
resultTail.prev = cur2;
cur2.prev = resultTailPrev;
if (resultTailPrev != null) {
resultTailPrev.next = cur2;
} else {
resultHead = cur2;
}
resultTailPrev = cur2;
// advance cur2
if (cur2next != null) {
cur2next.prev = null;
}
cur2 = cur2next;
break;
case 1:
// append into result
resultTail.next = cur2;
cur2.prev = resultTail;
resultTailPrev = resultTail;
resultTail = cur2;
// remove cur2
cur2 = cur2.next;
resultTail.next = null;
if (cur2 != null) {
cur2.prev = null;
}
break;
}
}
}
// record up to which point a suffix minimum update is needed
RootListNode updateSuffixFix = resultTail;
// here rank of cur1 is more than result rank
if (cur1 != null) {
cur1.prev = resultTail;
resultTail.next = cur1;
resultTail = rootList.tail;
}
// here rank of cur2 is more than result rank
if (cur2 != null) {
cur2.prev = resultTail;
resultTail.next = cur2;
resultTail = tail;
}
// update suffix minimum
updateSuffixMin(updateSuffixFix);
// store final list
rootList.head = resultHead;
rootList.tail = resultTail;
}
}