Mega Code Archive
An undirected graph that keeps track of connected components (groups)
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/**
* Copyright (c) 2008-2010 Morten Silcowitz.
*
* This file is part of the Jinngine physics library
*
* Jinngine is published under the GPL license, available
* at http://www.gnu.org/copyleft/gpl.html.
*/
//package jinngine.util;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Queue;
import java.util.Set;
/**
* An undirected graph that keeps track of connected components (groups). Each
* time an edge is added or removed from the graph, data structures are
* maintained, reflecting connected components in the graph. This means, that
* adding edges are roughly an O(k) operation, while removing an edge could i
* result in a total traversal of the graph, visiting all present edges, worst
* case O((n-1)^2) where n is the number of nodes. Usually this will be much
* cheaper, given that the graph has a low density, and is fragmented into
* separated components.
*
* @param <T>
* Type that stores in nodes
* @param <U>
* Type that stores in edges
*/
public class HashMapComponentGraph<T, U, V> implements ComponentGraph<T, U, V> {
// wrapping classes
private final class Node {
public Node(T element) {
this.element = element;
}
public final T element;
public int color;
public final int hashCode() {
return element.hashCode();
}
public final boolean equals(Object other) {
return element.equals(((Node) other).element);
}
}
// component wrapper class for the type V.
private final class Component {
private final V element;
public Component(V element) {
this.element = element;
}
public final int hashCode() {
return element.hashCode();
}
public final boolean equals(Object other) {
return element.equals(((Component) other).element);
}
}
// /**
// * Node classifier for the ContactGraph
// *
// * @param <T> Type that stores in nodes
// */
// public interface NodeClassifier<T> {
// /**
// * @param node Node to classify
// * @return true if the node is to be considered as a delimiting node, such
// that two
// * components in some graph, would not be merged if connected through such
// a node. Returns false otherwise.
// */
// public boolean isDelimitor(final T node);
// }
// this would ideally be a Set, but the HashSet implementation doesn't allow
// one to get the
// actual reference to a specific object in the set. This means that we
// can't keep our Node objects
// unique, which we would like to do
private final LinkedHashMap<Node, Node> allnodes = new LinkedHashMap<Node, Node>();
private final LinkedHashSet<Node> freenodes = new LinkedHashSet<Node>();//
private final Map<Node, Set<Node>> edges = new LinkedHashMap<Node, Set<Node>>();
private final Map<Node, Component> component = new LinkedHashMap<Node, Component>();
private final Map<Pair<T>, U> edgeData = new LinkedHashMap<Pair<T>, U>();//
private final Map<Component, Set<Node>> componentNodes = new LinkedHashMap<Component, Set<Node>>();//
private final Map<Component, Set<Pair<T>>> componentEdges = new LinkedHashMap<Component, Set<Pair<T>>>();//
private final NodeClassifier<T> nodeClassifier;
// TODO the nodes map is not cleaned up, nodes that are removed still
// remains in here
// default component creator
private final ComponentHandler<T, V> componenthandler;
// = new ComponentHandler<V>() {
// public V newComponent() {
// return null;
// };
// };
// /**
// * Create a new component graph
// * @param nodeClassifier a classifier for the type T, used for the
// connected components analysis
// */
// public HashMapComponentGraph( NodeClassifier<T> nodeClassifier ) {
// this.nodeClassifier = nodeClassifier;
// }
/**
* Create a new component graph
*
* @param nodeClassifier
* a classifier for the type T, used for the connected components
* analysis
* @param componetcreator
* a creator for new components that arrise inside the component
* graph
*/
public HashMapComponentGraph(NodeClassifier<T> nodeClassifier,
ComponentHandler<T, V> componentcreator) {
this.componenthandler = componentcreator;
this.nodeClassifier = nodeClassifier;
}
/**
* Add an edge to the graph, and implicitly add included end-nodes if not
* already present in the graph. This is roughly an O(k) and sometimes
* O(nodes) operation, depending on whether components are to be merged or
* not.
*
* @param pair
* A pair of nodes, where an edge is to be added between them.
* @param edgeelement
* An element of type U to store in the new edge
*/
@Override
public final void addEdge(Pair<T> pair, U edgeelement) {
// do not act if edge is already present
if (edgeData.containsKey(pair)) {
// update the edge data user reference
edgeData.put(pair, edgeelement);
// System.out.println("Edge already present");
return;
}
// add the new edge data to the edge
edgeData.put(pair, edgeelement);
// get nodes from the node tables ( in this way we can keep data other
// than T in the Node objects)
// if the nodes are not present, we add them to the allnodes and to
// freenodes
Node a = new Node(pair.getFirst());
if (allnodes.containsKey(a)) {
a = allnodes.get(a);
} else {
allnodes.put(a, a);
freenodes.add(a);
}
Node b = new Node(pair.getSecond());
if (allnodes.containsKey(b)) {
b = allnodes.get(b);
} else {
allnodes.put(b, b);
freenodes.add(b);
}
// if b is fixed, interchange a and b ( now, if b is fixed, both a and b
// are fixed)
if (nodeClassifier.isDelimitor(b.element)) {
Node t = a;
a = b;
b = t;
}
// add edge to nodes. First create hash sets, and then add the nodes to
// them
if (!edges.containsKey(a))
edges.put(a, new LinkedHashSet<Node>());
if (!edges.containsKey(b))
edges.put(b, new LinkedHashSet<Node>());
edges.get(b).add(a);
edges.get(a).add(b);
// Cases
// i. Both nodes are delimiters
// a) do nothing
// ii. One node is delimiter:
// a). non-delimiter is in a component
// do nothing
// b). non-delimiter is not in a component
// create a new component for the non-delimiter node
// iii. No node is delimiter:
// a). no node is in a component
// create a new component for both nodes
// b). one node is in a component
// add the new node to this component
// c). both nodes are in a component
// 1. the same component
// do nothing
// 2. different components
// merge the one component into the other
// case i a)
// both a and b are delimitors
if (nodeClassifier.isDelimitor(b.element)) {
// do nothing
// ii)
// one is delimiter
} else if (nodeClassifier.isDelimitor(a.element)) {
// if b is not in a group, create a new one for b
if (!component.containsKey(b)) {
// case ii b)
Component g = new Component(componenthandler.newComponent());
// add b to the new group
component.put(b, g);
componentNodes.put(g, new LinkedHashSet<Node>());
componentNodes.get(g).add(b);
// notify handler
componenthandler.nodeAddedToComponent(g.element, b.element);
// b is not a free node anymore
freenodes.remove(b);
// add to pairs
componentEdges.put(g, new LinkedHashSet<Pair<T>>());
componentEdges.get(g).add(pair);
// return;
} else {
// case ii a)
// add to pairs
Component g = component.get(b);
componentEdges.get(g).add(pair);
}
// non of the bodies are delimiters
} else {
// if b is in a group, interchange a and b
// ( now, if b is in a group, both a and b are grouped)
if (component.containsKey(b)) {
Node t = a;
a = b;
b = t;
}
// both in components
if (component.containsKey(b)) {
// same component
if (component.get(a) == component.get(b)) {
// do nothing
// add edge to this component
componentEdges.get(component.get(a)).add(pair);
// different components
} else {
// two nodes from two different components was connected.
// we then merge the two components into one
// merge groups (remove the gb group)
Component ga = component.get(a);
Component gb = component.get(b);
// call the user handler to say we are merging gb into ga
componenthandler.mergeComponent(ga.element, gb.element);
// update the component table, i.e. update bodies that was
// tied to component gb, to ga
Iterator<Node> i = componentNodes.get(gb).iterator();
while (i.hasNext()) {
Node body = i.next();
component.put(body, ga);
}
// put nodes in group b into group a
componentNodes.get(ga).addAll(componentNodes.get(gb));
componentEdges.get(ga).addAll(componentEdges.get(gb));
// also, add the new edge (pair)
componentEdges.get(ga).add(pair);
// remove the gb component from the component table
componentNodes.remove(gb);
componentEdges.remove(gb);
// return;
}
// one group
} else if (component.containsKey(a)) {
// assign b to the group of a
Component g = component.get(a);
component.put(b, g);
componentNodes.get(g).add(b);
componentEdges.get(g).add(pair);
// b is not a free node anymore
freenodes.remove(b);
// notify handler that b is added to the group of a
componenthandler.nodeAddedToComponent(g.element, b.element);
// return;
// no groups
} else {
// create a new component for both bodies
Component newGroup = new Component(
componenthandler.newComponent());
component.put(a, newGroup);
component.put(b, newGroup);
componentNodes.put(newGroup, new LinkedHashSet<Node>());
componentNodes.get(newGroup).add(a);
componentNodes.get(newGroup).add(b);
// notify handler that a and b is added to the new component
componenthandler.nodeAddedToComponent(newGroup.element,
a.element);
componenthandler.nodeAddedToComponent(newGroup.element,
b.element);
componentEdges.put(newGroup, new LinkedHashSet<Pair<T>>());
componentEdges.get(newGroup).add(pair);
// both a and b are not free now
freenodes.remove(a);
freenodes.remove(b);
// return;
}
}
// // System.out.println("After add: " + groups.keySet().size() +
// " groups with " + group.size() + " bodies" );
// Iterator<Component> groupiter = componentNodes.keySet().iterator();
//
// Set<Pair<T>> allpairs = new HashSet<Pair<T>>();
// Set<Node> allnodes = new HashSet<Node>();
// while(groupiter.hasNext()){
// Component g = groupiter.next();
// //System.out.println( "Group " + g + " : " + groupPairs.get(g).size()
// + " pairs " );
//
// Iterator<Pair<T>> pairiter = componentEdges.get(g).iterator();
// while (pairiter.hasNext()) {
// Pair<T> thispair = pairiter.next();
// //System.out.println( " pair:"+thispair.hashCode());
// if (allpairs.contains(thispair)) {
// System.out.println("Duplicates!!!!");
// System.exit(0);
// }
// allpairs.add(thispair);
//
// }
//
//
// Iterator<Node> nodeiter = componentNodes.get(g).iterator();
// while (nodeiter.hasNext()) {
// Node node = nodeiter.next();
// //System.out.println( " Node:"+node);
// if (allnodes.contains(node)) {
// System.out.println("Duplicates!!!!");
// System.exit(0);
// }
// allnodes.add(node);
//
// }
//
//
//
// }
}
/**
* Remove an edge. If the removal results in one or more isolated nodes,
* these will be removed from the graph implicitly.
*
* For non-dense and relatively fragmented graphs, this operation will be
* cheap. Otherwise, for dense and strongly connected graphs, the operation
* could include a full traversal of the graph visiting all present edges,
* resulting in an O((n-1)^2) operation, where n is the number of nodes in
* the graph.
*
* @param pair
* edge to be removed
* @return true if the edge was actually removed, false if the edge did not
* exists before call.
*/
@Override
public final boolean removeEdge(Pair<T> pair) {
// don't act if edge is not present
if (!edgeData.containsKey(pair)) {
// System.out.println("Edge NOT present");
return false;
} else {
edgeData.remove(pair);
}
// get the node out of the node adjacency hash map ( at this point we
// know that the nodes must
// exist, because the edge exists
Node a = new Node(pair.getFirst());
if (allnodes.containsKey(a)) {
a = allnodes.get(a);
} else {
// not possible
throw new IllegalStateException(
"ComponentGraph.removeEdge(): Node did not have an adjacency entry. ComponentGraph corrupted.");
}
Node b = new Node(pair.getSecond());
if (allnodes.containsKey(b)) {
b = allnodes.get(b);
} else {
// this is not possible
throw new IllegalStateException(
"ComponentGraph.removeEdge(): Node did not have an adjacency entry. ComponentGraph corrupted.");
}
// if b is fixed, interchange a and b ( now, if b is fixed, both a and b
// are fixed)
if (nodeClassifier.isDelimitor(b.element)) {
Node t = a;
a = b;
b = t;
}
// remove references to each node, in each nodes
// connected node sets
edges.get(a).remove(b);
edges.get(b).remove(a);
// if no edges left in set, remove the set
if (edges.get(a).isEmpty())
edges.remove(a);
// if no edges left in set, remove it
if (edges.get(b).isEmpty())
edges.remove(b);
// Cases
// i. Both node are delimiters
// do nothing
// ii. One node is delimiter:
// a). non-delimiter is in a component
// do nothing (node could now be alone in its component)
// if node contains no other edges, delete it from its component
// b). non-delimiter is not in a component (not possible)
// do nothing/ report fatal error
// iii. No node is delimiter:
// a). no node is in a component (not possible)
// do nothing/ error
// b). one node is in a component (not possible)
// do nothing
// c). both nodes are in a component
// 1. the same component
// remove edge, traverse breadth-first from each node to determine
// if component should be split.
// 2. different components (not possible)
// do nothing/ error
// both nodes are fixed
if (nodeClassifier.isDelimitor(b.element)) {
// do nothing
// return;
// one is fixed
} else if (nodeClassifier.isDelimitor(a.element)) {
if (component.containsKey(b)) { // only possible option
// System.out.println("One fixed node");
Component g = component.get(b);
// check for another edge on this node
if (!edges.containsKey(b)) {
// System.out.println("b did not have any edges");
// remove the node from component
component.remove(b);
// notify handler
componenthandler.nodeRemovedFromComponent(g.element,
b.element);
// b is now free
freenodes.add(b);
Set<Node> s = componentNodes.get(g);
if (!s.remove(b)) {
System.out.println("ALARM");
System.exit(0);
}
// remove group if empty
if (s.isEmpty()) {
// System.out.println("groups entry removed");
componentNodes.remove(g);
// TODO notify handler
} else {
System.out.println("Group isn't empty, why??");
// System.exit(0);
}
} else {
// b has edges left, and is part of a group. Were done
}
// remove edge from component (even if b was not removed from
// the group)
Set<Pair<T>> sp = componentEdges.get(g);
sp.remove(pair);
// remove group if empty
if (sp.isEmpty()) {
// System.out.println("grouppair entry removed " + g );
componentEdges.remove(g);
}
} else {
throw new IllegalStateException(
"HashMapComponentGraph.removeEdge(): A connected non-delimiter node was not in a component. ComponentGraph corrupted.");
}
// return;
// none is fixed
} else {
// if b has edges, interchange a and b
// ( now, if b has edges, both a and b have edges)
if (edges.containsKey(b)) {
Node t = a;
a = b;
b = t;
}
// both are in the same group (only possible option)
Component oldgroup = component.get(a);
if (oldgroup != component.get(b)) {
System.out.println("Different groups??!");
System.exit(0);
}
// both have edges
if (edges.containsKey(b)) {
final int NONE = 0;
final int RED = 1;
final int BLUE = 2;
// clear node colors in entire group
Iterator<Node> i = componentNodes.get(oldgroup).iterator();
while (i.hasNext()) {
i.next().color = NONE;
}
// perform breadth-first traversal,
// to determine if group has become disjoint
boolean disjoint = true;
Queue<Node> queue = new LinkedList<Node>();
Set<Pair<T>> blueEdges = new LinkedHashSet<Pair<T>>();
a.color = RED;
b.color = BLUE;
queue.add(a);
queue.add(b);
// traverse
while (!queue.isEmpty()) {
Node node = queue.poll();
// add nodes neighbors to queue
Iterator<Node> neighbors = edges.get(node).iterator();
while (neighbors.hasNext()) {
Node neighbor = neighbors.next();
// remember visited edges
if (node.color == BLUE)
blueEdges.add(new Pair<T>(node.element,
neighbor.element));
if (nodeClassifier.isDelimitor(neighbor.element)) {
// ignore fixed nodes
continue;
} else if (neighbor.color == NONE) {
neighbor.color = node.color;
queue.add(neighbor);
continue;
} else if (neighbor.color != node.color) {
// group is connected
disjoint = false;
break;
} else {
// already visited
continue;
}
} // while neighbors
} // while queue
// handle result of traversal
if (disjoint) {
// System.out.println("Splitting group");
// new group
Component newgroup = new Component(
componenthandler.newComponent());
Set<Node> blues = new LinkedHashSet<Node>();
// find all blue nodes
Iterator<Node> iter = componentNodes.get(oldgroup)
.iterator();
while (iter.hasNext()) {
Node node = iter.next();
if (node.color == BLUE) {
blues.add(node);
component.put(node, newgroup);
}
}
// impossible
if (blues.isEmpty()) {
System.out.println("Why was no blue nodes found?");
System.exit(0);
}
// remove bodies from old components and add the new
// component
componentNodes.get(oldgroup).removeAll(blues);
componentNodes.put(newgroup, blues);
// remove blue edges from the red group and create a new
// group with pairs (ng)
componentEdges.get(oldgroup).removeAll(blueEdges);
componentEdges.get(oldgroup).remove(pair); // the edge that
// was to be
// removed
componentEdges.put(newgroup, blueEdges);
// return;
} else {
// System.out.println("Group still connected");
// we keep group as it is, but remove the pair (edge)
Set<Pair<T>> sp = componentEdges.get(oldgroup);
sp.remove(pair);
// remove group if empty
if (sp.isEmpty()) {
// System.out.println("grouppair entry removed " +
// oldgroup );
componentEdges.remove(oldgroup);
}
// return;
}
// a has an edge and b do not
} else if (edges.containsKey(a)) {
// keep group as it is, but wipe out b
component.remove(b);
componentNodes.get(oldgroup).remove(b);
// b is now a free node
freenodes.add(b);
// notify handler that b is removed from oldgroup
componenthandler.nodeRemovedFromComponent(oldgroup.element,
b.element);
if (componentNodes.get(oldgroup).isEmpty()) { // never happens
System.out.println("How can group be empty?");
componentNodes.remove(oldgroup);
}
// remove from pairs
// System.out.println("removing " + pair +" from group pairs " +
// oldgroup);
Set<Pair<T>> sp = componentEdges.get(oldgroup);
sp.remove(pair);
// remove group if empty
if (sp.isEmpty()) {
// System.out.println("grouppair entry removed " + oldgroup
// );
componentEdges.remove(oldgroup);
}
// non have edges
} else {
// clear out group entirely
component.remove(a);
component.remove(b);
// both a and b are free nodes now
freenodes.add(a);
freenodes.add(b);
// notify handler that a and b is removed
componenthandler.nodeRemovedFromComponent(oldgroup.element,
a.element);
componenthandler.nodeRemovedFromComponent(oldgroup.element,
b.element);
// assume that the group is only containing a and b?
componentNodes.get(oldgroup).remove(b);
componentNodes.get(oldgroup).remove(a);
if (componentNodes.get(oldgroup).isEmpty()) {
componentNodes.remove(oldgroup);
} else { // impossible
System.out
.println("Hmm still stuff in group but no outgoing edges?"
+ componentNodes.get(oldgroup)
+ " a and b is " + a + ", " + b);
System.exit(0);
}
// remove from pairs
Set<Pair<T>> sp = componentEdges.get(oldgroup);
sp.remove(pair);
// remove group if empty
if (sp.isEmpty()) {
// System.out.println("grouppair entry removed " + oldgroup
// );
componentEdges.remove(oldgroup);
}
}// non have edges
} // none is fixed
// System.out.println("After remove: " + groups.keySet().size() +
// " groups with " + group.size() + " bodies" );
// Iterator<Component<V>> groupiter =
// componentNodes.keySet().iterator();
//
// Set<Pair<T>> allpairs = new HashSet<Pair<T>>();
// Set<Node> allnodes = new HashSet<Node>();
// while(groupiter.hasNext()){
// Component<V> g = groupiter.next();
// //System.out.println( "Group " + g + " : " + groupPairs.get(g).size()
// + " pairs " );
//
// Iterator<Pair<T>> pairiter = componentEdges.get(g).iterator();
// while (pairiter.hasNext()) {
// Pair<T> thispair = pairiter.next();
// //System.out.println( " pair:"+thispair.hashCode());
// if (allpairs.contains(thispair)) {
// System.out.println("Duplicates!!!!");
// System.exit(0);
// }
// allpairs.add(thispair);
//
// }
//
//
// Iterator<Node> nodeiter = componentNodes.get(g).iterator();
// while (nodeiter.hasNext()) {
// Node node = nodeiter.next();
// //System.out.println( " Node:"+node);
// if (allnodes.contains(node)) {
// System.out.println("Duplicates!!!!");
// System.exit(0);
// }
// allnodes.add(node);
//
// }
//
// }
return true;
}
@Override
public final U getEdge(Pair<T> pair) {
if (edgeData.containsKey(pair)) {
return edgeData.get(pair);
} else {
return null;
}
}
@Override
public final Iterator<V> getComponents() {
// wrapping iterator
return new Iterator<V>() {
private final Iterator<Component> iter = componentEdges.keySet()
.iterator();
public boolean hasNext() {
return iter.hasNext();
}
@Override
public V next() {
return iter.next().element;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
};
}
@Override
public final Iterator<U> getEdgesInComponent(V c) {
// get edges from component
final Set<Pair<T>> edges = componentEdges.get(new Component(c));
// abort if the component doesn't exist
if (edges == null)
return null;
// get the edges
final Iterator<Pair<T>> i = edges.iterator();
// create an iterator that wraps the process of picking out the
// edge data types from edgeData
return new Iterator<U>() {
@Override
public boolean hasNext() {
return i.hasNext();
}
@Override
public U next() {
if (i.hasNext()) {
Pair<T> p = i.next();
// return the edge data
return edgeData.get(p);
}
// no element available
return null;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
};
}
@Override
public Iterator<T> getNodesInComponent(V c1) {
// get edges from component
final Set<Node> nodes = componentNodes.get(new Component(c1));
// abort if the component doesn't exist
if (nodes == null)
return null;
// get the edges
final Iterator<Node> i = nodes.iterator();
// create an iterator iterates the nodes, but return the T element value
return new Iterator<T>() {
@Override
public boolean hasNext() {
return i.hasNext();
}
@Override
public T next() {
if (i.hasNext()) {
Node p = i.next();
// return the node data
return p.element;
}
// no element available
return null;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
};
}
/**
* Auxiliary method to print the graph
*/
public final void print() {
System.out.println("Status: " + componentNodes.keySet().size()
+ " components with " + component.size() + " bodies, "
+ getNumberOfFreeNodes() + " free ");
Iterator<Component> groupiter = componentNodes.keySet().iterator();
Set<Pair<T>> allpairs = new LinkedHashSet<Pair<T>>();
Set<Node> allnodes = new LinkedHashSet<Node>();
while (groupiter.hasNext()) {
Component g = groupiter.next();
System.out.println("Group " + g.element + " : "
+ componentEdges.get(g).size() + " pairs, "
+ componentNodes.get(g).size() + " nodes ");
Iterator<Pair<T>> pairiter = componentEdges.get(g).iterator();
while (pairiter.hasNext()) {
Pair<T> thispair = pairiter.next();
// System.out.println( " pair:"+thispair.hashCode());
if (allpairs.contains(thispair)) {
System.out.println("Duplicates!!!!");
System.exit(0);
}
allpairs.add(thispair);
}
Iterator<Node> nodeiter = componentNodes.get(g).iterator();
while (nodeiter.hasNext()) {
Node node = nodeiter.next();
// System.out.println( " Node:"+node);
if (allnodes.contains(node)) {
System.out.println("Duplicates!!!!");
System.exit(0);
}
allnodes.add(node);
}
}
}
@Override
public int getNumberOfComponents() {
// return the number of keys in the component-Nodes map
return componentNodes.keySet().size();
}
@Override
public Iterator<T> getConnectedNodes(final T node) {
// create a wrap iterator
return new Iterator<T>() {
Iterator<Node> i = edges.get(new Node(node)).iterator();
@Override
public boolean hasNext() {
return i.hasNext();
}
@Override
public T next() {
return i.next().element;
}
@Override
public void remove() {
}
};
}
public void addNode(T nodeelement) {
// check if we know about this node
Node node = new Node(nodeelement);
if (allnodes.containsKey(node)) {
// ignore. Maybe give warning?
System.out
.println("HashMapComponentGraph.addNode(): Node is already in graph");
} else {
// add to both allnodes and freenodes
allnodes.put(node, node);
freenodes.add(node);
}
}
public void removeNode(T nodeelement) {
Node node = new Node(nodeelement);
// check if node is in freenodes. If so, we don't have to do anything
// but removing the node
// from both freenodes and allnodes
if (freenodes.contains(node)) {
freenodes.remove(node);
allnodes.remove(node);
return;
}
// we now expect node to be part of a component, but we can now simply
// remove all incident
// edges to the node. After that, the node will be placed into
// freenodes, and we can trivially
// remove it
// remove each incident edges. store edges in intermediate list to avoid
// concurrent modification errors
List<Pair<T>> edgesToRemove = new ArrayList<Pair<T>>();
Iterator<T> neighbors = getConnectedNodes(node.element);
while (neighbors.hasNext()) {
Pair<T> nodepair = new Pair<T>(node.element, neighbors.next());
edgesToRemove.add(nodepair);
}
for (Pair<T> edge : edgesToRemove)
removeEdge(edge);
// we can now remove the node
if (freenodes.contains(node)) {
freenodes.remove(node);
allnodes.remove(node);
return;
} else {
System.out
.println("HashMapComponentGraph.removeNode(): Node was not free after removing its edges");
}
}
@Override
public int getNumberOfNodes() {
return allnodes.size();
}
@Override
public int getNumberOfFreeNodes() {
return freenodes.size();
}
@Override
public Iterator<T> getFreeNodes() {
// wrapping iterator
return new Iterator<T>() {
Iterator<Node> i = freenodes.iterator();
@Override
public boolean hasNext() {
return i.hasNext();
}
@Override
public T next() {
return i.next().element;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
};
}
@Override
public Iterator<U> getConnectedEdges(final T node) {
if (edges.containsKey(new Node(node))) {
// create a wrap iterator
return new Iterator<U>() {
Set<Node> outEdges = edges.get(new Node(node));
Iterator<Node> i = outEdges.iterator();
@Override
public boolean hasNext() {
return i.hasNext();
}
@Override
public U next() {
// create a edge pair from the node types, and return the
// edge data
return edgeData.get(new Pair<T>(node, i.next().element));
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
};
} else {
// create a dummy empty iterator
return new Iterator<U>() {
@Override
public boolean hasNext() {
return false;
}
@Override
public U next() {
return null;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
};
}
}
}
/**
* Copyright (c) 2008-2010 Morten Silcowitz.
*
* This file is part of the Jinngine physics library
*
* Jinngine is published under the GPL license, available at
* http://www.gnu.org/copyleft/gpl.html.
*/
// package jinngine.util;
// import java.util.Iterator;
/**
* An undirected graph that keeps track of connected components (groups). Each
* time an edge is added or removed from the graph, data structures are
* maintained, reflecting connected components in the graph. This means, that
* adding edges are roughly an O(k) operation, while removing an edge could i
* result in a total traversal of the graph, visiting all present edges, worst
* case O((n-1)^2) where n is the number of nodes. Usually this will be much
* cheaper, given that the graph has a low density, and is fragmented into
* separated components.
*
* @param <T>
* Type that stores in nodes
* @param <U>
* Type that stores in edges
* @param <V>
* Type that stores in components
*/
interface ComponentGraph<T, U, V> {
/**
* Interface for supplying custom component objects. Components are used to
* reference the independently connected components in the graph. It is
* therefore useful to be able to store user information within the
* component references.
*/
public interface ComponentHandler<T, V> {
/**
* Called when a new component is created. This call MUST return a
* unique object of type V, that has not been previously known to the
* ComponentGraph
*
* @return a new unique component of type V
*/
public V newComponent();
/**
* Called prior to two components being merged. This gives the user a
* way to manipulate data in the component type V. During this call, it
* is possible to access the data of the ComponentGraph in a read-only
* fashion.
*
* @param remaining
* The component that will be the union of both components
* after merge
* @param disappearing
* The component that will be removed from the graph
*/
public void mergeComponent(V remaining, V leaving);
/**
* Called when a node is added to some component
*/
public void nodeAddedToComponent(V component, T node);
/**
* Called when a node is removed from some component
*/
public void nodeRemovedFromComponent(V component, T node);
}
/**
* Node classifier for the ContactGraph
*
* @param <T>
* Type that stores in nodes
*/
public interface NodeClassifier<T> {
/**
* @param node
* Node to classify
* @return true if the node is to be considered as a delimiting node,
* such that two components in some graph, would not be merged
* if connected through such a node. Returns false otherwise.
*/
public boolean isDelimitor(final T node);
}
/**
* Add a node to the graph. If the node already exists in the graph, the
* call will have no effect.
*
* @param node
*/
public void addNode(T node);
/**
* Remove a node from the graph. All edges incident to this node will be
* removed as well.
*
* @param node
*/
public void removeNode(T node);
/**
* Add an edge to the graph, and implicitly add included end-nodes if not
* already present in the graph. This is roughly an O(k) and sometimes
* O(nodes) operation, depending on whether components are to be merged or
* not.
*
* @param pair
* A pair of nodes, where an edge is to be added between them.
* @param edgeelement
* An element of type U to store in the new edge
*/
public void addEdge(Pair<T> pair, U edgeelement);
/**
* Remove an edge. If the removal results in one or more isolated nodes,
* these will be removed from the graph implicitly.
*
* For non-dense and relatively fragmented graphs, this operation will be
* cheap. Otherwise, for dense and strongly connected graphs, the operation
* could include a full traversal of the graph visiting all present edges,
* resulting in an O((n-1)^2) operation, where n is the number of nodes in
* the graph.
*
* @param pair
* edge to be removed
* @return true if the edge was actually removed, false if the edge did not
* exists before call.
*/
public boolean removeEdge(Pair<T> pair);
/**
* Get the edge element of type U that is stored in the edge defined by a
* pair of node types T. If no such edge exist, the return value is null.
*
* @param pair
* A pair of T type objects defining an edge in the graph
* @return The U type object stored in the edge. Return value is null if no
* such edge is present in the graph
*/
public U getEdge(Pair<T> pair);
/**
* Return an iterator yielding the edges in the specified component.
*
* @param c
* Component to iterate
* @return Iterator giving the edge elements in the component
*/
public Iterator<U> getEdgesInComponent(V c);
/**
* Returns an iterator yielding the nodes present in the given component
*
* @param c
* Any component of this graph
* @return An iterator yielding the nodes present in the component c
*/
public Iterator<T> getNodesInComponent(V c);
/**
* Return an iterator that yields the components in the graph
*
* @return
*/
public Iterator<V> getComponents();
/**
* Return the number of components in this graph
*/
public int getNumberOfComponents();
/**
* Return the total number of nodes in this graph
*/
public int getNumberOfNodes();
/**
* Return the number of free nodes, which are nodes that are not a part of a
* graph component
*/
public int getNumberOfFreeNodes();
/**
* Get all free nodes. A free node is not in any component.
*/
public Iterator<T> getFreeNodes();
/**
* Get all nodes that is connected to the given node. The constructible
* pairs Pair<T> can then be used to obtain the edge type U using
* getEdge(Pair<T>)
*/
public Iterator<T> getConnectedNodes(T node);
/**
* Get all edges connected to the given node
*
* @param node
* @return An iterator over all edges connected to the given node
*/
public Iterator<U> getConnectedEdges(T node);
}
/**
* Copyright (c) 2008-2010 Morten Silcowitz.
*
* This file is part of the Jinngine physics library
*
* Jinngine is published under the GPL license, available at
* http://www.gnu.org/copyleft/gpl.html.
*/
// package jinngine.util;
/**
* Small pair class, for the purpose of indexing unordered pairs in a hash table
*/
final class Pair<T> {
private final T o1;
private final T o2;
public Pair(T o1, T o2) {
this.o1 = o1;
this.o2 = o2;
}
// since this is an unordered pair, we use
// the same hash code for interchanced objects
@Override
public final int hashCode() {
return o1.hashCode() * o2.hashCode();
}
@SuppressWarnings("unchecked")
@Override
public final boolean equals(Object other) {
if (this == other)
return true;
if (other == null)
return false;
if (other instanceof Pair) {
final Pair<T> otherpair = (Pair<T>) other;
return ((o1.equals(otherpair.o1) && o2.equals(otherpair.o2)) || (o1
.equals(otherpair.o2) && o2.equals(otherpair.o1)));
} else {
return false;
}
}
public final T getFirst() {
return o1;
}
public final T getSecond() {
return o2;
}
public final boolean contains(T o) {
return (o == o1 || o == o2);
}
}
]]>