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