com.mxgraph.analysis.mxFibonacciHeap Maven / Gradle / Ivy
/**
* Copyright (c) 2007, Gaudenz Alder
*/
package com.mxgraph.analysis;
import java.util.Hashtable;
import java.util.Map;
/**
* This class implements a priority queue.
*/
public class mxFibonacciHeap
{
/**
* Maps from elements to nodes
*/
protected Map nodes = new Hashtable();
/**
*
*/
protected Node min;
/**
*
*/
protected int size;
/**
* Returns the node that represents element.
*/
public Node getNode(Object element, boolean create)
{
Node node = nodes.get(element);
if (node == null && create)
{
node = new Node(element, Double.MAX_VALUE);
nodes.put(element, node);
insert(node, node.getKey());
}
return node;
}
/**
* Returns true if the queue is empty.
*/
public boolean isEmpty()
{
return min == null;
}
/**
* 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 whose value should be decreased.
* @param k New key value for node x.
*
* @exception IllegalArgumentException
* Thrown if k is larger than x.key value.
*/
public void decreaseKey(Node x, double k)
{
if (k > x.key)
{
throw new IllegalArgumentException(
"decreaseKey() got larger key value");
}
x.key = k;
Node y = x.parent;
if ((y != null) && (x.key < y.key))
{
cut(x, y);
cascadingCut(y);
}
if (min == null || x.key < min.key)
{
min = x;
}
}
/**
* 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 The node to remove from the heap.
*/
public void delete(Node x)
{
// make x as small as possible
decreaseKey(x, Double.NEGATIVE_INFINITY);
// remove the smallest, which decreases n also
removeMin();
}
/**
* 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(Node node, double key)
{
node.key = key;
// concatenate node into min list
if (min != null)
{
node.left = min;
node.right = min.right;
min.right = node;
node.right.left = node;
if (key < min.key)
{
min = node;
}
}
else
{
min = node;
}
size++;
}
/**
* Returns the smallest element in the heap. This smallest element is the
* one with the minimum key value.
*
*
* Running time: O(1) actual
*
*
* @return Returns the heap node with the smallest key.
*/
public Node min()
{
return min;
}
/**
* Removes the smallest element from the heap. This will cause the trees in
* the heap to be consolidated, if necessary.
* Does not remove the data node so that the current key remains stored.
*
*
* Running time: O(log n) amortized
*
*
* @return Returns the node with the smallest key.
*/
public Node removeMin()
{
Node z = min;
if (z != null)
{
int numKids = z.degree;
Node x = z.child;
Node 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 = min;
x.right = min.right;
min.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)
{
min = null;
}
else
{
min = z.right;
consolidate();
}
// decrement size of heap
size--;
}
return z;
}
/**
* Returns the size of the heap which is measured in the number of elements
* contained in the heap.
*
*
* Running time: O(1) actual
*
*
* @return Returns the number of elements in the heap.
*/
public int size()
{
return 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 The first heap.
* @param h2 The second heap.
* @return Returns a new heap containing h1 and h2.
*/
public static mxFibonacciHeap union(mxFibonacciHeap h1, mxFibonacciHeap h2)
{
mxFibonacciHeap h = new mxFibonacciHeap();
if ((h1 != null) && (h2 != null))
{
h.min = h1.min;
if (h.min != null)
{
if (h2.min != null)
{
h.min.right.left = h2.min.left;
h2.min.left.right = h.min.right;
h.min.right = h2.min;
h2.min.left = h.min;
if (h2.min.key < h1.min.key)
{
h.min = h2.min;
}
}
}
else
{
h.min = h2.min;
}
h.size = h1.size + h2.size;
}
return h;
}
/**
* 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 The node to perform cascading cut on.
*/
protected void cascadingCut(Node y)
{
Node 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);
}
}
}
/**
* Consolidates the trees in the heap by joining trees of equal degree until
* there are no more trees of equal degree in the root list.
*
*
* Running time: O(log n) amortized
*
*/
protected void consolidate()
{
int arraySize = size + 1;
Node[] array = new Node[arraySize];
// Initialize degree array
for (int i = 0; i < arraySize; i++)
{
array[i] = null;
}
// Find the number of root nodes.
int numRoots = 0;
Node x = min;
if (x != null)
{
numRoots++;
x = x.right;
while (x != min)
{
numRoots++;
x = x.right;
}
}
// For each node in root list do...
while (numRoots > 0)
{
// Access this node's degree..
int d = x.degree;
Node next = x.right;
// ..and see if there's another of the same degree.
while (array[d] != null)
{
// There is, make one of the nodes a child of the other.
Node y = array[d];
// Do this based on the key value.
if (x.key > y.key)
{
Node temp = y;
y = x;
x = temp;
}
// Node y disappears from root list.
link(y, x);
// We've handled this degree, go to next one.
array[d] = null;
d++;
}
// Save this node for later when we might encounter another
// of the same degree.
array[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[].
min = null;
for (int i = 0; i < arraySize; i++)
{
if (array[i] != null)
{
// We've got a live one, add it to root list.
if (min != null)
{
// First remove node from root list.
array[i].left.right = array[i].right;
array[i].right.left = array[i].left;
// Now add to root list, again.
array[i].left = min;
array[i].right = min.right;
min.right = array[i];
array[i].right.left = array[i];
// Check if this is a new min.
if (array[i].key < min.key)
{
min = array[i];
}
}
else
{
min = array[i];
}
}
}
}
/**
* 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 The child of y to be removed from y's child list.
* @param y The parent of x about to lose a child.
*/
protected void cut(Node x, Node 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 = min;
x.right = min.right;
min.right = x;
x.right.left = x;
// set parent[x] to nil
x.parent = null;
// set mark[x] to false
x.mark = false;
}
/**
* Make node y a child of node x.
*
*
* Running time: O(1) actual
*
*
* @param y The node to become child.
* @param x The node to become parent.
*/
protected void link(Node y, Node 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;
}
/**
* Implements a node of the Fibonacci heap. It holds the information
* necessary for maintaining the structure of the heap. It also holds the
* reference to the key value (which is used to determine the heap
* structure). Additional Node data should be stored in a subclass.
*/
public static class Node
{
Object userObject;
/**
* first child node
*/
Node child;
/**
* left sibling node
*/
Node left;
/**
* parent node
*/
Node parent;
/**
* right sibling node
*/
Node right;
/**
* true if this node has had a child removed since this node was added
* to its parent
*/
boolean mark;
/**
* key value for this node
*/
double key;
/**
* number of children of this node (does not count grandchildren)
*/
int degree;
/**
* Default constructor. Initializes the right and left pointers, making
* this a circular doubly-linked list.
*
* @param key The initial key for node.
*/
public Node(Object userObject, double key)
{
this.userObject = userObject;
right = this;
left = this;
this.key = key;
}
/**
* Obtain the key for this node.
*
* @return the key
*/
public final double getKey()
{
return key;
}
/**
* @return Returns the userObject.
*/
public Object getUserObject()
{
return userObject;
}
/**
* @param userObject The userObject to set.
*/
public void setUserObject(Object userObject)
{
this.userObject = userObject;
}
}
}
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