org.jgrapht.util.FibonacciHeap Maven / Gradle / Ivy
/* ==========================================
* JGraphT : a free Java graph-theory library
* ==========================================
*
* Project Info: http://jgrapht.sourceforge.net/
* Project Creator: Barak Naveh ([email protected])
*
* (C) Copyright 2003-2008, by Barak Naveh and Contributors.
*
* This program and the accompanying materials are dual-licensed under
* either
*
* (a) the terms of the GNU Lesser General Public License version 2.1
* as published by the Free Software Foundation, or (at your option) any
* later version.
*
* or (per the licensee's choosing)
*
* (b) the terms of the Eclipse Public License v1.0 as published by
* the Eclipse Foundation.
*/
/* --------------------------
* FibonnaciHeap.java
* --------------------------
* (C) Copyright 1999-2003, by Nathan Fiedler and Contributors.
*
* Original Author: Nathan Fiedler
* Contributor(s): John V. Sichi
*
* $Id$
*
* Changes
* -------
* 03-Sept-2003 : Adapted from Nathan Fiedler (JVS);
*
* Name Date Description
* ---- ---- -----------
* nf 08/31/97 Initial version
* nf 09/07/97 Removed FibHeapData interface
* nf 01/20/01 Added synchronization
* nf 01/21/01 Made Node an inner class
* nf 01/05/02 Added clear(), renamed empty() to
* isEmpty(), and renamed printHeap()
* to toString()
* nf 01/06/02 Removed all synchronization
*
*/
package org.jgrapht.util;
import java.util.*;
/**
* This class implements a Fibonacci heap data structure. Much of the code in
* this class is based on the algorithms in the "Introduction to Algorithms"by
* Cormen, Leiserson, and Rivest in Chapter 21. The amortized running time of
* most of these methods is O(1), making it a very fast data structure. Several
* have an actual running time of O(1). removeMin() and delete() have O(log n)
* amortized running times because they do the heap consolidation. If you
* attempt to store nodes in this heap with key values of -Infinity
* (Double.NEGATIVE_INFINITY) the delete() operation may fail to
* remove the correct element.
*
* Note that this implementation is not synchronized. If multiple
* threads access a set concurrently, and at least one of the threads modifies
* the set, it must be synchronized externally. This is typically
* accomplished by synchronizing on some object that naturally encapsulates the
* set.
*
* This class was originally developed by Nathan Fiedler for the GraphMaker
* project. It was imported to JGraphT with permission, courtesy of Nathan
* Fiedler.
*
* @author Nathan Fiedler
*/
public class FibonacciHeap
{
private static final double oneOverLogPhi =
1.0 / Math.log((1.0 + Math.sqrt(5.0)) / 2.0);
/**
* Points to the minimum node in the heap.
*/
private FibonacciHeapNode minNode;
/**
* Number of nodes in the heap.
*/
private int nNodes;
/**
* Constructs a FibonacciHeap object that contains no elements.
*/
public FibonacciHeap()
{
} // FibonacciHeap
/**
* Tests if the Fibonacci heap is empty or not. Returns true if the heap is
* empty, false otherwise.
*
* Running time: O(1) actual
*
* @return true if the heap is empty, false otherwise
*/
public boolean isEmpty()
{
return minNode == null;
}
// isEmpty
/**
* Removes all elements from this heap.
*/
public void clear()
{
minNode = null;
nNodes = 0;
}
// clear
/**
* Decreases the key value for a heap node, given the new value to take on.
* The structure of the heap may be changed and will not be consolidated.
*
* Running time: O(1) amortized
*
* @param x node to decrease the key of
* @param k new key value for node x
*
* @exception IllegalArgumentException Thrown if k is larger than x.key
* value.
*/
public void decreaseKey(FibonacciHeapNode x, double k)
{
if (k > x.key) {
throw new IllegalArgumentException(
"decreaseKey() got larger key value");
}
x.key = k;
FibonacciHeapNode y = x.parent;
if ((y != null) && (x.key < y.key)) {
cut(x, y);
cascadingCut(y);
}
if (x.key < minNode.key) {
minNode = x;
}
}
// decreaseKey
/**
* Deletes a node from the heap given the reference to the node. The trees
* in the heap will be consolidated, if necessary. This operation may fail
* to remove the correct element if there are nodes with key value
* -Infinity.
*
* Running time: O(log n) amortized
*
* @param x node to remove from heap
*/
public void delete(FibonacciHeapNode x)
{
// make x as small as possible
decreaseKey(x, Double.NEGATIVE_INFINITY);
// remove the smallest, which decreases n also
removeMin();
}
// delete
/**
* Inserts a new data element into the heap. No heap consolidation is
* performed at this time, the new node is simply inserted into the root
* list of this heap.
*
* Running time: O(1) actual
*
* @param node new node to insert into heap
* @param key key value associated with data object
*/
public void insert(FibonacciHeapNode node, double key)
{
node.key = key;
// concatenate node into min list
if (minNode != null) {
node.left = minNode;
node.right = minNode.right;
minNode.right = node;
node.right.left = node;
if (key < minNode.key) {
minNode = node;
}
} else {
minNode = node;
}
nNodes++;
}
// insert
/**
* Returns the smallest element in the heap. This smallest element is the
* one with the minimum key value.
*
* Running time: O(1) actual
*
* @return heap node with the smallest key
*/
public FibonacciHeapNode min()
{
return minNode;
}
// min
/**
* Removes the smallest element from the heap. This will cause the trees in
* the heap to be consolidated, if necessary.
*
* Running time: O(log n) amortized
*
* @return node with the smallest key
*/
public FibonacciHeapNode removeMin()
{
FibonacciHeapNode z = minNode;
if (z != null) {
int numKids = z.degree;
FibonacciHeapNode x = z.child;
FibonacciHeapNode tempRight;
// for each child of z do...
while (numKids > 0) {
tempRight = x.right;
// remove x from child list
x.left.right = x.right;
x.right.left = x.left;
// add x to root list of heap
x.left = minNode;
x.right = minNode.right;
minNode.right = x;
x.right.left = x;
// set parent[x] to null
x.parent = null;
x = tempRight;
numKids--;
}
// remove z from root list of heap
z.left.right = z.right;
z.right.left = z.left;
if (z == z.right) {
minNode = null;
} else {
minNode = z.right;
consolidate();
}
// decrement size of heap
nNodes--;
}
return z;
}
// removeMin
/**
* Returns the size of the heap which is measured in the number of elements
* contained in the heap.
*
* Running time: O(1) actual
*
* @return number of elements in the heap
*/
public int size()
{
return nNodes;
}
// size
/**
* Joins two Fibonacci heaps into a new one. No heap consolidation is
* performed at this time. The two root lists are simply joined together.
*
* Running time: O(1) actual
*
* @param h1 first heap
* @param h2 second heap
*
* @return new heap containing h1 and h2
*/
public static FibonacciHeap union(
FibonacciHeap h1,
FibonacciHeap h2)
{
FibonacciHeap h = new FibonacciHeap();
if ((h1 != null) && (h2 != null)) {
h.minNode = h1.minNode;
if (h.minNode != null) {
if (h2.minNode != null) {
h.minNode.right.left = h2.minNode.left;
h2.minNode.left.right = h.minNode.right;
h.minNode.right = h2.minNode;
h2.minNode.left = h.minNode;
if (h2.minNode.key < h1.minNode.key) {
h.minNode = h2.minNode;
}
}
} else {
h.minNode = h2.minNode;
}
h.nNodes = h1.nNodes + h2.nNodes;
}
return h;
}
// union
/**
* Creates a String representation of this Fibonacci heap.
*
* @return String of this.
*/
@Override public String toString()
{
if (minNode == null) {
return "FibonacciHeap=[]";
}
// create a new stack and put root on it
Stack> stack = new Stack>();
stack.push(minNode);
StringBuffer buf = new StringBuffer(512);
buf.append("FibonacciHeap=[");
// do a simple breadth-first traversal on the tree
while (!stack.empty()) {
FibonacciHeapNode curr = stack.pop();
buf.append(curr);
buf.append(", ");
if (curr.child != null) {
stack.push(curr.child);
}
FibonacciHeapNode start = curr;
curr = curr.right;
while (curr != start) {
buf.append(curr);
buf.append(", ");
if (curr.child != null) {
stack.push(curr.child);
}
curr = curr.right;
}
}
buf.append(']');
return buf.toString();
}
// toString
/**
* Performs a cascading cut operation. This cuts y from its parent and then
* does the same for its parent, and so on up the tree.
*
* Running time: O(log n); O(1) excluding the recursion
*
* @param y node to perform cascading cut on
*/
protected void cascadingCut(FibonacciHeapNode y)
{
FibonacciHeapNode z = y.parent;
// if there's a parent...
if (z != null) {
// if y is unmarked, set it marked
if (!y.mark) {
y.mark = true;
} else {
// it's marked, cut it from parent
cut(y, z);
// cut its parent as well
cascadingCut(z);
}
}
}
// cascadingCut
protected void consolidate()
{
int arraySize =
((int) Math.floor(Math.log(nNodes) * oneOverLogPhi)) + 1;
List> array =
new ArrayList>(arraySize);
// Initialize degree array
for (int i = 0; i < arraySize; i++) {
array.add(null);
}
// Find the number of root nodes.
int numRoots = 0;
FibonacciHeapNode x = minNode;
if (x != null) {
numRoots++;
x = x.right;
while (x != minNode) {
numRoots++;
x = x.right;
}
}
// For each node in root list do...
while (numRoots > 0) {
// Access this node's degree..
int d = x.degree;
FibonacciHeapNode next = x.right;
// ..and see if there's another of the same degree.
for (;;) {
FibonacciHeapNode y = array.get(d);
if (y == null) {
// Nope.
break;
}
// There is, make one of the nodes a child of the other.
// Do this based on the key value.
if (x.key > y.key) {
FibonacciHeapNode temp = y;
y = x;
x = temp;
}
// FibonacciHeapNode y disappears from root list.
link(y, x);
// We've handled this degree, go to next one.
array.set(d, null);
d++;
}
// Save this node for later when we might encounter another
// of the same degree.
array.set(d, x);
// Move forward through list.
x = next;
numRoots--;
}
// Set min to null (effectively losing the root list) and
// reconstruct the root list from the array entries in array[].
minNode = null;
for (int i = 0; i < arraySize; i++) {
FibonacciHeapNode y = array.get(i);
if (y == null) {
continue;
}
// We've got a live one, add it to root list.
if (minNode != null) {
// First remove node from root list.
y.left.right = y.right;
y.right.left = y.left;
// Now add to root list, again.
y.left = minNode;
y.right = minNode.right;
minNode.right = y;
y.right.left = y;
// Check if this is a new min.
if (y.key < minNode.key) {
minNode = y;
}
} else {
minNode = y;
}
}
}
// consolidate
/**
* The reverse of the link operation: removes x from the child list of y.
* This method assumes that min is non-null.
*
* Running time: O(1)
*
* @param x child of y to be removed from y's child list
* @param y parent of x about to lose a child
*/
protected void cut(FibonacciHeapNode x, FibonacciHeapNode y)
{
// remove x from childlist of y and decrement degree[y]
x.left.right = x.right;
x.right.left = x.left;
y.degree--;
// reset y.child if necessary
if (y.child == x) {
y.child = x.right;
}
if (y.degree == 0) {
y.child = null;
}
// add x to root list of heap
x.left = minNode;
x.right = minNode.right;
minNode.right = x;
x.right.left = x;
// set parent[x] to nil
x.parent = null;
// set mark[x] to false
x.mark = false;
}
// cut
/**
* Make node y a child of node x.
*
* Running time: O(1) actual
*
* @param y node to become child
* @param x node to become parent
*/
protected void link(FibonacciHeapNode y, FibonacciHeapNode x)
{
// remove y from root list of heap
y.left.right = y.right;
y.right.left = y.left;
// make y a child of x
y.parent = x;
if (x.child == null) {
x.child = y;
y.right = y;
y.left = y;
} else {
y.left = x.child;
y.right = x.child.right;
x.child.right = y;
y.right.left = y;
}
// increase degree[x]
x.degree++;
// set mark[y] false
y.mark = false;
}
// link
}
// FibonacciHeap