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/*
* Copyright (C) 2016 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.INNER_CAPACITY;
import static com.google.common.graph.GraphConstants.INNER_LOAD_FACTOR;
import static com.google.common.graph.Graphs.checkNonNegative;
import static com.google.common.graph.Graphs.checkPositive;
import com.google.common.base.Function;
import com.google.common.collect.AbstractIterator;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterators;
import com.google.common.collect.UnmodifiableIterator;
import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.concurrent.atomic.AtomicBoolean;
import javax.annotation.CheckForNull;
/**
* An implementation of {@link GraphConnections} for directed graphs.
*
* @author James Sexton
* @author Jens Nyman
* @param Node parameter type
* @param Value parameter type
*/
@ElementTypesAreNonnullByDefault
final class DirectedGraphConnections implements GraphConnections {
/**
* A wrapper class to indicate a node is both a predecessor and successor while still providing
* the successor value.
*/
private static final class PredAndSucc {
private final Object successorValue;
PredAndSucc(Object successorValue) {
this.successorValue = successorValue;
}
}
/**
* A value class representing single connection between the origin node and another node.
*
* There can be two types of connections (predecessor and successor), which is represented by
* the two implementations.
*/
private abstract static class NodeConnection {
final N node;
NodeConnection(N node) {
this.node = checkNotNull(node);
}
static final class Pred extends NodeConnection {
Pred(N node) {
super(node);
}
@Override
public boolean equals(@CheckForNull Object that) {
if (that instanceof Pred) {
return this.node.equals(((Pred) that).node);
} else {
return false;
}
}
@Override
public int hashCode() {
// Adding the class hashCode to avoid a clash with Succ instances.
return Pred.class.hashCode() + node.hashCode();
}
}
static final class Succ extends NodeConnection {
Succ(N node) {
super(node);
}
@Override
public boolean equals(@CheckForNull Object that) {
if (that instanceof Succ) {
return this.node.equals(((Succ) that).node);
} else {
return false;
}
}
@Override
public int hashCode() {
// Adding the class hashCode to avoid a clash with Pred instances.
return Succ.class.hashCode() + node.hashCode();
}
}
}
private static final Object PRED = new Object();
// Every value in this map must either be an instance of PredAndSucc with a successorValue of
// type V, PRED (representing predecessor), or an instance of type V (representing successor).
private final Map adjacentNodeValues;
/**
* All node connections in this graph, in edge insertion order.
*
* Note: This field and {@link #adjacentNodeValues} cannot be combined into a single
* LinkedHashMap because one target node may be mapped to both a predecessor and a successor. A
* LinkedHashMap combines two such edges into a single node-value pair, even though the edges may
* not have been inserted consecutively.
*/
@CheckForNull private final List> orderedNodeConnections;
private int predecessorCount;
private int successorCount;
private DirectedGraphConnections(
Map adjacentNodeValues,
@CheckForNull List> orderedNodeConnections,
int predecessorCount,
int successorCount) {
this.adjacentNodeValues = checkNotNull(adjacentNodeValues);
this.orderedNodeConnections = orderedNodeConnections;
this.predecessorCount = checkNonNegative(predecessorCount);
this.successorCount = checkNonNegative(successorCount);
checkState(
predecessorCount <= adjacentNodeValues.size()
&& successorCount <= adjacentNodeValues.size());
}
static DirectedGraphConnections of(ElementOrder incidentEdgeOrder) {
// We store predecessors and successors in the same map, so double the initial capacity.
int initialCapacity = INNER_CAPACITY * 2;
List> orderedNodeConnections;
switch (incidentEdgeOrder.type()) {
case UNORDERED:
orderedNodeConnections = null;
break;
case STABLE:
orderedNodeConnections = new ArrayList<>();
break;
default:
throw new AssertionError(incidentEdgeOrder.type());
}
return new DirectedGraphConnections<>(
/* adjacentNodeValues = */ new HashMap(initialCapacity, INNER_LOAD_FACTOR),
orderedNodeConnections,
/* predecessorCount = */ 0,
/* successorCount = */ 0);
}
static DirectedGraphConnections ofImmutable(
N thisNode, Iterable> incidentEdges, Function successorNodeToValueFn) {
checkNotNull(thisNode);
checkNotNull(successorNodeToValueFn);
Map adjacentNodeValues = new HashMap<>();
ImmutableList.Builder> orderedNodeConnectionsBuilder =
ImmutableList.builder();
int predecessorCount = 0;
int successorCount = 0;
for (EndpointPair incidentEdge : incidentEdges) {
if (incidentEdge.nodeU().equals(thisNode) && incidentEdge.nodeV().equals(thisNode)) {
// incidentEdge is a self-loop
adjacentNodeValues.put(thisNode, new PredAndSucc(successorNodeToValueFn.apply(thisNode)));
orderedNodeConnectionsBuilder.add(new NodeConnection.Pred<>(thisNode));
orderedNodeConnectionsBuilder.add(new NodeConnection.Succ<>(thisNode));
predecessorCount++;
successorCount++;
} else if (incidentEdge.nodeV().equals(thisNode)) { // incidentEdge is an inEdge
N predecessor = incidentEdge.nodeU();
Object existingValue = adjacentNodeValues.put(predecessor, PRED);
if (existingValue != null) {
adjacentNodeValues.put(predecessor, new PredAndSucc(existingValue));
}
orderedNodeConnectionsBuilder.add(new NodeConnection.Pred<>(predecessor));
predecessorCount++;
} else { // incidentEdge is an outEdge
checkArgument(incidentEdge.nodeU().equals(thisNode));
N successor = incidentEdge.nodeV();
V value = successorNodeToValueFn.apply(successor);
Object existingValue = adjacentNodeValues.put(successor, value);
if (existingValue != null) {
checkArgument(existingValue == PRED);
adjacentNodeValues.put(successor, new PredAndSucc(value));
}
orderedNodeConnectionsBuilder.add(new NodeConnection.Succ<>(successor));
successorCount++;
}
}
return new DirectedGraphConnections<>(
adjacentNodeValues,
orderedNodeConnectionsBuilder.build(),
predecessorCount,
successorCount);
}
@Override
public Set adjacentNodes() {
if (orderedNodeConnections == null) {
return Collections.unmodifiableSet(adjacentNodeValues.keySet());
} else {
return new AbstractSet() {
@Override
public UnmodifiableIterator iterator() {
Iterator> nodeConnections = orderedNodeConnections.iterator();
Set seenNodes = new HashSet<>();
return new AbstractIterator() {
@Override
@CheckForNull
protected N computeNext() {
while (nodeConnections.hasNext()) {
NodeConnection nodeConnection = nodeConnections.next();
boolean added = seenNodes.add(nodeConnection.node);
if (added) {
return nodeConnection.node;
}
}
return endOfData();
}
};
}
@Override
public int size() {
return adjacentNodeValues.size();
}
@Override
public boolean contains(@CheckForNull Object obj) {
return adjacentNodeValues.containsKey(obj);
}
};
}
}
@Override
public Set predecessors() {
return new AbstractSet() {
@Override
public UnmodifiableIterator iterator() {
if (orderedNodeConnections == null) {
Iterator> entries = adjacentNodeValues.entrySet().iterator();
return new AbstractIterator() {
@Override
@CheckForNull
protected N computeNext() {
while (entries.hasNext()) {
Entry entry = entries.next();
if (isPredecessor(entry.getValue())) {
return entry.getKey();
}
}
return endOfData();
}
};
} else {
Iterator> nodeConnections = orderedNodeConnections.iterator();
return new AbstractIterator() {
@Override
@CheckForNull
protected N computeNext() {
while (nodeConnections.hasNext()) {
NodeConnection nodeConnection = nodeConnections.next();
if (nodeConnection instanceof NodeConnection.Pred) {
return nodeConnection.node;
}
}
return endOfData();
}
};
}
}
@Override
public int size() {
return predecessorCount;
}
@Override
public boolean contains(@CheckForNull Object obj) {
return isPredecessor(adjacentNodeValues.get(obj));
}
};
}
@Override
public Set successors() {
return new AbstractSet() {
@Override
public UnmodifiableIterator iterator() {
if (orderedNodeConnections == null) {
Iterator> entries = adjacentNodeValues.entrySet().iterator();
return new AbstractIterator() {
@Override
@CheckForNull
protected N computeNext() {
while (entries.hasNext()) {
Entry entry = entries.next();
if (isSuccessor(entry.getValue())) {
return entry.getKey();
}
}
return endOfData();
}
};
} else {
Iterator> nodeConnections = orderedNodeConnections.iterator();
return new AbstractIterator() {
@Override
@CheckForNull
protected N computeNext() {
while (nodeConnections.hasNext()) {
NodeConnection nodeConnection = nodeConnections.next();
if (nodeConnection instanceof NodeConnection.Succ) {
return nodeConnection.node;
}
}
return endOfData();
}
};
}
}
@Override
public int size() {
return successorCount;
}
@Override
public boolean contains(@CheckForNull Object obj) {
return isSuccessor(adjacentNodeValues.get(obj));
}
};
}
@Override
public Iterator> incidentEdgeIterator(N thisNode) {
checkNotNull(thisNode);
Iterator> resultWithDoubleSelfLoop;
if (orderedNodeConnections == null) {
resultWithDoubleSelfLoop =
Iterators.concat(
Iterators.transform(
predecessors().iterator(),
(N predecessor) -> EndpointPair.ordered(predecessor, thisNode)),
Iterators.transform(
successors().iterator(),
(N successor) -> EndpointPair.ordered(thisNode, successor)));
} else {
resultWithDoubleSelfLoop =
Iterators.transform(
orderedNodeConnections.iterator(),
(NodeConnection connection) -> {
if (connection instanceof NodeConnection.Succ) {
return EndpointPair.ordered(thisNode, connection.node);
} else {
return EndpointPair.ordered(connection.node, thisNode);
}
});
}
AtomicBoolean alreadySeenSelfLoop = new AtomicBoolean(false);
return new AbstractIterator>() {
@Override
@CheckForNull
protected EndpointPair computeNext() {
while (resultWithDoubleSelfLoop.hasNext()) {
EndpointPair edge = resultWithDoubleSelfLoop.next();
if (edge.nodeU().equals(edge.nodeV())) {
if (!alreadySeenSelfLoop.getAndSet(true)) {
return edge;
}
} else {
return edge;
}
}
return endOfData();
}
};
}
@SuppressWarnings("unchecked")
@Override
@CheckForNull
public V value(N node) {
checkNotNull(node);
Object value = adjacentNodeValues.get(node);
if (value == PRED) {
return null;
}
if (value instanceof PredAndSucc) {
return (V) ((PredAndSucc) value).successorValue;
}
return (V) value;
}
@SuppressWarnings("unchecked")
@Override
public void removePredecessor(N node) {
checkNotNull(node);
Object previousValue = adjacentNodeValues.get(node);
boolean removedPredecessor;
if (previousValue == PRED) {
adjacentNodeValues.remove(node);
removedPredecessor = true;
} else if (previousValue instanceof PredAndSucc) {
adjacentNodeValues.put((N) node, ((PredAndSucc) previousValue).successorValue);
removedPredecessor = true;
} else {
removedPredecessor = false;
}
if (removedPredecessor) {
checkNonNegative(--predecessorCount);
if (orderedNodeConnections != null) {
orderedNodeConnections.remove(new NodeConnection.Pred<>(node));
}
}
}
@SuppressWarnings("unchecked")
@Override
@CheckForNull
public V removeSuccessor(Object node) {
checkNotNull(node);
Object previousValue = adjacentNodeValues.get(node);
Object removedValue;
if (previousValue == null || previousValue == PRED) {
removedValue = null;
} else if (previousValue instanceof PredAndSucc) {
adjacentNodeValues.put((N) node, PRED);
removedValue = ((PredAndSucc) previousValue).successorValue;
} else { // successor
adjacentNodeValues.remove(node);
removedValue = previousValue;
}
if (removedValue != null) {
checkNonNegative(--successorCount);
if (orderedNodeConnections != null) {
orderedNodeConnections.remove(new NodeConnection.Succ<>((N) node));
}
}
/*
* TODO(cpovirk): `return (V) removedValue` once our checker permits that.
*
* (We promoted a class of warnings into errors because sometimes they indicate real problems.
* But now we need to "undo" some instance of spurious errors, as discussed in
* https://github.com/jspecify/checker-framework/issues/8.)
*/
return removedValue == null ? null : (V) removedValue;
}
@Override
public void addPredecessor(N node, V unused) {
Object previousValue = adjacentNodeValues.put(node, PRED);
boolean addedPredecessor;
if (previousValue == null) {
addedPredecessor = true;
} else if (previousValue instanceof PredAndSucc) {
// Restore previous PredAndSucc object.
adjacentNodeValues.put(node, previousValue);
addedPredecessor = false;
} else if (previousValue != PRED) { // successor
// Do NOT use method parameter value 'unused'. In directed graphs, successors store the value.
adjacentNodeValues.put(node, new PredAndSucc(previousValue));
addedPredecessor = true;
} else {
addedPredecessor = false;
}
if (addedPredecessor) {
checkPositive(++predecessorCount);
if (orderedNodeConnections != null) {
orderedNodeConnections.add(new NodeConnection.Pred<>(node));
}
}
}
@SuppressWarnings("unchecked")
@Override
@CheckForNull
public V addSuccessor(N node, V value) {
Object previousValue = adjacentNodeValues.put(node, value);
Object previousSuccessor;
if (previousValue == null) {
previousSuccessor = null;
} else if (previousValue instanceof PredAndSucc) {
adjacentNodeValues.put(node, new PredAndSucc(value));
previousSuccessor = ((PredAndSucc) previousValue).successorValue;
} else if (previousValue == PRED) {
adjacentNodeValues.put(node, new PredAndSucc(value));
previousSuccessor = null;
} else { // successor
previousSuccessor = previousValue;
}
if (previousSuccessor == null) {
checkPositive(++successorCount);
if (orderedNodeConnections != null) {
orderedNodeConnections.add(new NodeConnection.Succ<>(node));
}
}
// See the comment on the similar cast in removeSuccessor.
return previousSuccessor == null ? null : (V) previousSuccessor;
}
private static boolean isPredecessor(@CheckForNull Object value) {
return (value == PRED) || (value instanceof PredAndSucc);
}
private static boolean isSuccessor(@CheckForNull Object value) {
return (value != PRED) && (value != null);
}
}