/*******************************************************************************
* Copyright (c) 2002 - 2006 IBM Corporation.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package com.ibm.wala.util.graph.traverse;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import com.ibm.wala.util.Predicate;
import com.ibm.wala.util.collections.HashMapFactory;
import com.ibm.wala.util.collections.HashSetFactory;
import com.ibm.wala.util.collections.NonNullSingletonIterator;
import com.ibm.wala.util.graph.Graph;
/**
* This class searches breadth-first for node that matches some criteria. If found, it reports a path to the first node found.
*
* This class follows the outNodes of the graph nodes to define the graph, but this behavior can be changed by overriding the
* getConnected method.
*
* TODO: if finding many paths, use a dynamic programming algorithm instead of calling this repeatedly.
*/
public class BFSPathFinder<T> {
private final boolean DEBUG = false;
/**
* The graph to search
*/
final private Graph<T> G;
/**
* The Filter which defines the target set of nodes to find
*/
final private Predicate<T> filter;
/**
* an enumeration of all nodes to search from
*/
final private Iterator<T> roots;
/**
* Construct a breadth-first enumerator starting with a particular node in a directed graph.
*
* @param G the graph whose nodes to enumerate
*/
public BFSPathFinder(Graph<T> G, T N, Predicate<T> f) {
if (G == null) {
throw new IllegalArgumentException("G is null");
}
if (f == null) {
throw new IllegalArgumentException("null f");
}
this.G = G;
this.roots = new NonNullSingletonIterator<T>(N);
this.filter = f;
}
/**
* Construct a breadth-first enumerator starting with a particular node in a directed graph.
*
* @param G the graph whose nodes to enumerate
* @throws IllegalArgumentException if G is null
*/
public BFSPathFinder(Graph<T> G, T src, final T target) throws IllegalArgumentException {
if (G == null) {
throw new IllegalArgumentException("G is null");
}
this.G = G;
this.roots = new NonNullSingletonIterator<T>(src);
if (!G.containsNode(src)) {
throw new IllegalArgumentException("src is not in graph " + src);
}
this.filter = new Predicate<T>() {
@Override public boolean test(T o) {
return target.equals(o);
}
};
}
/**
* Construct a breadth-first enumerator starting with a particular node in a directed graph.
*
* @param G the graph whose nodes to enumerate
*/
public BFSPathFinder(Graph<T> G, T src, Iterator<T> targets) {
if (targets == null) {
throw new IllegalArgumentException("targets is null");
}
final Set<T> ts = HashSetFactory.make();
while (targets.hasNext()) {
ts.add(targets.next());
}
this.G = G;
this.roots = new NonNullSingletonIterator<T>(src);
this.filter = new Predicate<T>() {
@Override public boolean test(T o) {
return ts.contains(o);
}
};
}
/**
* Construct a breadth-first enumerator starting with any of a set of nodes in a directed graph.
*
* @param G the graph whose nodes to enumerate
*/
public BFSPathFinder(Graph<T> G, Iterator<T> sources, final T target) {
if (G == null) {
throw new IllegalArgumentException("G is null");
}
if (sources == null) {
throw new IllegalArgumentException("sources is null");
}
this.G = G;
this.roots = sources;
this.filter = new Predicate<T>() {
@Override public boolean test(T o) {
return target.equals(o);
}
};
}
/**
* Construct a breadth-first enumerator across the (possibly improper) subset of nodes reachable from the nodes in the given
* enumeration.
*
* @param nodes the set of nodes from which to start searching
*/
public BFSPathFinder(Graph<T> G, Iterator<T> nodes, Predicate<T> f) {
this.G = G;
this.roots = nodes;
this.filter = f;
if (G == null) {
throw new IllegalArgumentException("G is null");
}
if (roots == null) {
throw new IllegalArgumentException("roots is null");
}
}
/**
* @return a List of nodes that specifies the first path found from a root to a node accepted by the filter. Returns null if no
* path found.
*/
public List<T> find() {
LinkedList<T> Q = new LinkedList<T>();
HashMap<Object, T> history = HashMapFactory.make();
while (roots.hasNext()) {
T next = roots.next();
Q.addLast(next);
history.put(next, null);
}
while (!Q.isEmpty()) {
T N = Q.removeFirst();
if (DEBUG) {
System.err.println(("visit " + N));
}
if (filter.test(N)) {
return makePath(N, history);
}
Iterator<? extends T> children = getConnected(N);
while (children.hasNext()) {
T c = children.next();
if (!history.containsKey(c)) {
Q.addLast(c);
history.put(c, N);
}
}
}
return null;
}
/**
* @return a List which represents a path in the breadth-first search to Q[i]. Q holds the nodes visited during the BFS, in order.
*/
private List<T> makePath(T node, Map<Object, T> history) {
ArrayList<T> result = new ArrayList<T>();
T n = node;
result.add(n);
while (true) {
T parent = history.get(n);
if (parent == null)
return result;
else {
result.add(parent);
n = parent;
}
}
}
/**
* get the out edges of a given node
*
* @param n the node of which to get the out edges
* @return the out edges
*
*/
protected Iterator<? extends T> getConnected(T n) {
return G.getSuccNodes(n);
}
}