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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 static com.google.common.graph.GraphConstants.ENDPOINTS_MISMATCH;
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 javax.annotation.CheckForNull;
/**
* This class provides a skeletal implementation of {@link BaseGraph}.
*
* <p>The methods implemented in this class should not be overridden unless the subclass admits a
* more efficient implementation.
*
* @author James Sexton
* @param <N> Node parameter type
*/
@ElementTypesAreNonnullByDefault
abstract class AbstractBaseGraph<N> implements BaseGraph<N> {
/**
* Returns the number of edges in this graph; used to calculate the size of {@link Graph#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 Graph#nodes()} and
* {@link #successors(Object)}.
*/
@Override
public Set<EndpointPair<N>> edges() {
return new AbstractSet<EndpointPair<N>>() {
@Override
public UnmodifiableIterator<EndpointPair<N>> iterator() {
return EndpointPairIterator.of(AbstractBaseGraph.this);
}
@Override
public int size() {
return Ints.saturatedCast(edgeCount());
}
@Override
public boolean remove(@CheckForNull 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<ArrayList> in a
// Graph<LinkedList>.
@SuppressWarnings("unchecked")
@Override
public boolean contains(@CheckForNull Object obj) {
if (!(obj instanceof EndpointPair)) {
return false;
}
EndpointPair<?> endpointPair = (EndpointPair<?>) obj;
return isOrderingCompatible(endpointPair)
&& nodes().contains(endpointPair.nodeU())
&& successors((N) endpointPair.nodeU()).contains(endpointPair.nodeV());
}
};
}
@Override
public ElementOrder<N> incidentEdgeOrder() {
return ElementOrder.unordered();
}
@Override
public Set<EndpointPair<N>> incidentEdges(N node) {
checkNotNull(node);
checkArgument(nodes().contains(node), "Node %s is not an element of this graph.", node);
return new IncidentEdgeSet<N>(this, node) {
@Override
public UnmodifiableIterator<EndpointPair<N>> iterator() {
if (graph.isDirected()) {
return Iterators.unmodifiableIterator(
Iterators.concat(
Iterators.transform(
graph.predecessors(node).iterator(),
(N predecessor) -> 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(),
(N successor) -> EndpointPair.ordered(node, successor))));
} else {
return Iterators.unmodifiableIterator(
Iterators.transform(
graph.adjacentNodes(node).iterator(),
(N adjacentNode) -> EndpointPair.unordered(node, adjacentNode)));
}
}
};
}
@Override
public int degree(N node) {
if (isDirected()) {
return IntMath.saturatedAdd(predecessors(node).size(), successors(node).size());
} else {
Set<N> 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);
}
@Override
public boolean hasEdgeConnecting(EndpointPair<N> endpoints) {
checkNotNull(endpoints);
if (!isOrderingCompatible(endpoints)) {
return false;
}
N nodeU = endpoints.nodeU();
N nodeV = endpoints.nodeV();
return nodes().contains(nodeU) && successors(nodeU).contains(nodeV);
}
/**
* Throws {@code IllegalArgumentException} if the ordering of {@code endpoints} is not compatible
* with the directionality of this graph.
*/
protected final void validateEndpoints(EndpointPair<?> endpoints) {
checkNotNull(endpoints);
checkArgument(isOrderingCompatible(endpoints), ENDPOINTS_MISMATCH);
}
/**
* Returns {@code true} iff {@code endpoints}' ordering is compatible with the directionality of
* this graph.
*/
protected final boolean isOrderingCompatible(EndpointPair<?> endpoints) {
return endpoints.isOrdered() == this.isDirected();
}
}
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