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/*
* Copyright (C) 2017 The Guava Authors
*
* Licensed 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.google.common.graph;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import com.google.common.base.Function;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterators;
import com.google.common.collect.Sets;
import com.google.common.collect.UnmodifiableIterator;
import com.google.common.math.IntMath;
import com.google.common.primitives.Ints;
import java.util.AbstractSet;
import java.util.Set;
import org.checkerframework.checker.nullness.compatqual.NullableDecl;
/**
* This class provides a skeletal implementation of {@link BaseGraph}.
*
* The methods implemented in this class should not be overridden unless the subclass admits a
* more efficient implementation.
*
* @author James Sexton
* @param Node parameter type
*/
abstract class AbstractBaseGraph implements BaseGraph {
/**
* Returns the number of edges in this graph; used to calculate the size of {@link #edges()}. This
* implementation requires O(|N|) time. Classes extending this one may manually keep track of the
* number of edges as the graph is updated, and override this method for better performance.
*/
protected long edgeCount() {
long degreeSum = 0L;
for (N node : nodes()) {
degreeSum += degree(node);
}
// According to the degree sum formula, this is equal to twice the number of edges.
checkState((degreeSum & 1) == 0);
return degreeSum >>> 1;
}
/**
* An implementation of {@link BaseGraph#edges()} defined in terms of {@link #nodes()} and {@link
* #successors(Object)}.
*/
@Override
public Set> edges() {
return new AbstractSet>() {
@Override
public UnmodifiableIterator> iterator() {
return EndpointPairIterator.of(AbstractBaseGraph.this);
}
@Override
public int size() {
return Ints.saturatedCast(edgeCount());
}
@Override
public boolean remove(Object o) {
throw new UnsupportedOperationException();
}
// Mostly safe: We check contains(u) before calling successors(u), so we perform unsafe
// operations only in weird cases like checking for an EndpointPair in a
// Graph.
@SuppressWarnings("unchecked")
@Override
public boolean contains(@NullableDecl Object obj) {
if (!(obj instanceof EndpointPair)) {
return false;
}
EndpointPair endpointPair = (EndpointPair) obj;
return isDirected() == endpointPair.isOrdered()
&& nodes().contains(endpointPair.nodeU())
&& successors((N) endpointPair.nodeU()).contains(endpointPair.nodeV());
}
};
}
@Override
public Set> incidentEdges(N node) {
checkNotNull(node);
checkArgument(nodes().contains(node), "Node %s is not an element of this graph.", node);
return IncidentEdgeSet.of(this, node);
}
@Override
public int degree(N node) {
if (isDirected()) {
return IntMath.saturatedAdd(predecessors(node).size(), successors(node).size());
} else {
Set neighbors = adjacentNodes(node);
int selfLoopCount = (allowsSelfLoops() && neighbors.contains(node)) ? 1 : 0;
return IntMath.saturatedAdd(neighbors.size(), selfLoopCount);
}
}
@Override
public int inDegree(N node) {
return isDirected() ? predecessors(node).size() : degree(node);
}
@Override
public int outDegree(N node) {
return isDirected() ? successors(node).size() : degree(node);
}
@Override
public boolean hasEdgeConnecting(N nodeU, N nodeV) {
checkNotNull(nodeU);
checkNotNull(nodeV);
return nodes().contains(nodeU) && successors(nodeU).contains(nodeV);
}
private abstract static class IncidentEdgeSet extends AbstractSet> {
protected final N node;
protected final BaseGraph graph;
public static IncidentEdgeSet of(BaseGraph graph, N node) {
return graph.isDirected() ? new Directed<>(graph, node) : new Undirected<>(graph, node);
}
private IncidentEdgeSet(BaseGraph graph, N node) {
this.graph = graph;
this.node = node;
}
@Override
public boolean remove(Object o) {
throw new UnsupportedOperationException();
}
private static final class Directed extends IncidentEdgeSet {
private Directed(BaseGraph graph, N node) {
super(graph, node);
}
@Override
public UnmodifiableIterator> iterator() {
return Iterators.unmodifiableIterator(
Iterators.concat(
Iterators.transform(
graph.predecessors(node).iterator(),
new Function>() {
@Override
public EndpointPair apply(N predecessor) {
return EndpointPair.ordered(predecessor, node);
}
}),
Iterators.transform(
// filter out 'node' from successors (already covered by predecessors, above)
Sets.difference(graph.successors(node), ImmutableSet.of(node)).iterator(),
new Function>() {
@Override
public EndpointPair apply(N successor) {
return EndpointPair.ordered(node, successor);
}
})));
}
@Override
public int size() {
return graph.inDegree(node)
+ graph.outDegree(node)
- (graph.successors(node).contains(node) ? 1 : 0);
}
@Override
public boolean contains(@NullableDecl Object obj) {
if (!(obj instanceof EndpointPair)) {
return false;
}
EndpointPair endpointPair = (EndpointPair) obj;
if (!endpointPair.isOrdered()) {
return false;
}
Object source = endpointPair.source();
Object target = endpointPair.target();
return (node.equals(source) && graph.successors(node).contains(target))
|| (node.equals(target) && graph.predecessors(node).contains(source));
}
}
private static final class Undirected extends IncidentEdgeSet {
private Undirected(BaseGraph graph, N node) {
super(graph, node);
}
@Override
public UnmodifiableIterator> iterator() {
return Iterators.unmodifiableIterator(
Iterators.transform(
graph.adjacentNodes(node).iterator(),
new Function>() {
@Override
public EndpointPair apply(N adjacentNode) {
return EndpointPair.unordered(node, adjacentNode);
}
}));
}
@Override
public int size() {
return graph.adjacentNodes(node).size();
}
@Override
public boolean contains(@NullableDecl Object obj) {
if (!(obj instanceof EndpointPair)) {
return false;
}
EndpointPair endpointPair = (EndpointPair) obj;
if (endpointPair.isOrdered()) {
return false;
}
Set adjacent = graph.adjacentNodes(node);
Object nodeU = endpointPair.nodeU();
Object nodeV = endpointPair.nodeV();
return (node.equals(nodeV) && adjacent.contains(nodeU))
|| (node.equals(nodeU) && adjacent.contains(nodeV));
}
}
}
}