com.hazelcast.org.apache.calcite.util.graph.BreadthFirstIterator Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to you under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.hazelcast.org.apache.calcite.util.graph;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
/**
* Iterates over the vertices in a directed graph in breadth-first order.
*
* @param Vertex type
* @param Edge type
*/
public class BreadthFirstIterator
implements Iterator {
private final DirectedGraph graph;
private final Deque deque = new ArrayDeque<>();
private final Set set = new HashSet<>();
public BreadthFirstIterator(DirectedGraph graph, V root) {
this.graph = graph;
this.deque.add(root);
}
public static Iterable of(
final DirectedGraph graph, final V root) {
return () -> new BreadthFirstIterator<>(graph, root);
}
/** Populates a set with the nodes reachable from a given node. */
public static void reachable(Set set,
final DirectedGraph graph, final V root) {
final Deque deque = new ArrayDeque<>();
deque.add(root);
set.add(root);
while (!deque.isEmpty()) {
V v = deque.removeFirst();
for (E e : graph.getOutwardEdges(v)) {
@SuppressWarnings("unchecked") V target = (V) e.target;
if (set.add(target)) {
deque.addLast(target);
}
}
}
}
public boolean hasNext() {
return !deque.isEmpty();
}
public V next() {
V v = deque.removeFirst();
for (E e : graph.getOutwardEdges(v)) {
@SuppressWarnings("unchecked") V target = (V) e.target;
if (set.add(target)) {
deque.addLast(target);
}
}
return v;
}
public void remove() {
throw new UnsupportedOperationException();
}
}