/*
* Copyright (C) 2014 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 com.google.common.annotations.Beta;
import com.google.common.base.Optional;
import java.util.Set;
import javax.annotation.Nullable;
/**
* An interface for <a
* href="https://en.wikipedia.org/wiki/Graph_(discrete_mathematics)">graph</a>-structured data,
* whose edges are unique objects.
*
* <p>A graph is composed of a set of nodes and a set of edges connecting pairs of nodes.
*
* <p>There are three primary interfaces provided to represent graphs. In order of increasing
* complexity they are: {@link Graph}, {@link ValueGraph}, and {@link Network}. You should generally
* prefer the simplest interface that satisfies your use case. See the <a
* href="https://github.com/google/guava/wiki/GraphsExplained#choosing-the-right-graph-type">
* "Choosing the right graph type"</a> section of the Guava User Guide for more details.
*
* <h3>Capabilities</h3>
*
* <p>{@code Network} supports the following use cases (<a
* href="https://github.com/google/guava/wiki/GraphsExplained#definitions">definitions of
* terms</a>):
*
* <ul>
* <li>directed graphs
* <li>undirected graphs
* <li>graphs that do/don't allow parallel edges
* <li>graphs that do/don't allow self-loops
* <li>graphs whose nodes/edges are insertion-ordered, sorted, or unordered
* <li>graphs whose edges are unique objects
* </ul>
*
* <h3>Building a {@code Network}</h3>
*
* <p>The implementation classes that `common.graph` provides are not public, by design. To create
* an instance of one of the built-in implementations of {@code Network}, use the {@link
* NetworkBuilder} class:
*
* <pre>{@code
* MutableNetwork<Integer, MyEdge> graph = NetworkBuilder.directed().build();
* }</pre>
*
* <p>{@link NetworkBuilder#build()} returns an instance of {@link MutableNetwork}, which is a
* subtype of {@code Network} that provides methods for adding and removing nodes and edges. If you
* do not need to mutate a graph (e.g. if you write a method than runs a read-only algorithm on the
* graph), you should use the non-mutating {@link Network} interface, or an {@link
* ImmutableNetwork}.
*
* <p>You can create an immutable copy of an existing {@code Network} using {@link
* ImmutableNetwork#copyOf(Network)}:
*
* <pre>{@code
* ImmutableNetwork<Integer, MyEdge> immutableGraph = ImmutableNetwork.copyOf(graph);
* }</pre>
*
* <p>Instances of {@link ImmutableNetwork} do not implement {@link MutableNetwork} (obviously!) and
* are contractually guaranteed to be unmodifiable and thread-safe.
*
* <p>The Guava User Guide has <a
* href="https://github.com/google/guava/wiki/GraphsExplained#building-graph-instances">more
* information on (and examples of) building graphs</a>.
*
* <h3>Additional documentation</h3>
*
* <p>See the Guava User Guide for the {@code common.graph} package (<a
* href="https://github.com/google/guava/wiki/GraphsExplained">"Graphs Explained"</a>) for
* additional documentation, including:
*
* <ul>
* <li><a
* href="https://github.com/google/guava/wiki/GraphsExplained#equals-hashcode-and-graph-equivalence">
* {@code equals()}, {@code hashCode()}, and graph equivalence</a>
* <li><a href="https://github.com/google/guava/wiki/GraphsExplained#synchronization">
* Synchronization policy</a>
* <li><a href="https://github.com/google/guava/wiki/GraphsExplained#notes-for-implementors">Notes
* for implementors</a>
* </ul>
*
* @author James Sexton
* @author Joshua O'Madadhain
* @param <N> Node parameter type
* @param <E> Edge parameter type
* @since 20.0
*/
// TODO(b/35456940): Update the documentation to reflect the new interfaces
@Beta
public interface Network<N, E> extends SuccessorsFunction<N>, PredecessorsFunction<N> {
//
// Network-level accessors
//
/** Returns all nodes in this network, in the order specified by {@link #nodeOrder()}. */
Set<N> nodes();
/** Returns all edges in this network, in the order specified by {@link #edgeOrder()}. */
Set<E> edges();
/**
* Returns a live view of this network as a {@link Graph}. The resulting {@link Graph} will have
* an edge connecting node A to node B if this {@link Network} has an edge connecting A to B.
*
* <p>If this network {@link #allowsParallelEdges() allows parallel edges}, parallel edges will be
* treated as if collapsed into a single edge. For example, the {@link #degree(Object)} of a node
* in the {@link Graph} view may be less than the degree of the same node in this {@link Network}.
*/
Graph<N> asGraph();
//
// Network properties
//
/**
* Returns true if the edges in this network are directed. Directed edges connect a {@link
* EndpointPair#source() source node} to a {@link EndpointPair#target() target node}, while
* undirected edges connect a pair of nodes to each other.
*/
boolean isDirected();
/**
* Returns true if this network allows parallel edges. Attempting to add a parallel edge to a
* network that does not allow them will throw an {@link IllegalArgumentException}.
*/
boolean allowsParallelEdges();
/**
* Returns true if this network allows self-loops (edges that connect a node to itself).
* Attempting to add a self-loop to a network that does not allow them will throw an {@link
* IllegalArgumentException}.
*/
boolean allowsSelfLoops();
/** Returns the order of iteration for the elements of {@link #nodes()}. */
ElementOrder<N> nodeOrder();
/** Returns the order of iteration for the elements of {@link #edges()}. */
ElementOrder<E> edgeOrder();
//
// Element-level accessors
//
/**
* Returns the nodes which have an incident edge in common with {@code node} in this network.
*
* @throws IllegalArgumentException if {@code node} is not an element of this network
*/
Set<N> adjacentNodes(N node);
/**
* Returns all nodes in this network adjacent to {@code node} which can be reached by traversing
* {@code node}'s incoming edges <i>against</i> the direction (if any) of the edge.
*
* <p>In an undirected network, this is equivalent to {@link #adjacentNodes(Object)}.
*
* @throws IllegalArgumentException if {@code node} is not an element of this network
*/
@Override
Set<N> predecessors(N node);
/**
* Returns all nodes in this network adjacent to {@code node} which can be reached by traversing
* {@code node}'s outgoing edges in the direction (if any) of the edge.
*
* <p>In an undirected network, this is equivalent to {@link #adjacentNodes(Object)}.
*
* <p>This is <i>not</i> the same as "all nodes reachable from {@code node} by following outgoing
* edges". For that functionality, see {@link Graphs#reachableNodes(Graph, Object)}.
*
* @throws IllegalArgumentException if {@code node} is not an element of this network
*/
@Override
Set<N> successors(N node);
/**
* Returns the edges whose {@link #incidentNodes(Object) incident nodes} in this network include
* {@code node}.
*
* @throws IllegalArgumentException if {@code node} is not an element of this network
*/
Set<E> incidentEdges(N node);
/**
* Returns all edges in this network which can be traversed in the direction (if any) of the edge
* to end at {@code node}.
*
* <p>In a directed network, an incoming edge's {@link EndpointPair#target()} equals {@code node}.
*
* <p>In an undirected network, this is equivalent to {@link #incidentEdges(Object)}.
*
* @throws IllegalArgumentException if {@code node} is not an element of this network
*/
Set<E> inEdges(N node);
/**
* Returns all edges in this network which can be traversed in the direction (if any) of the edge
* starting from {@code node}.
*
* <p>In a directed network, an outgoing edge's {@link EndpointPair#source()} equals {@code node}.
*
* <p>In an undirected network, this is equivalent to {@link #incidentEdges(Object)}.
*
* @throws IllegalArgumentException if {@code node} is not an element of this network
*/
Set<E> outEdges(N node);
/**
* Returns the count of {@code node}'s {@link #incidentEdges(Object) incident edges}, counting
* self-loops twice (equivalently, the number of times an edge touches {@code node}).
*
* <p>For directed networks, this is equal to {@code inDegree(node) + outDegree(node)}.
*
* <p>For undirected networks, this is equal to {@code incidentEdges(node).size()} + (number of
* self-loops incident to {@code node}).
*
* <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}.
*
* @throws IllegalArgumentException if {@code node} is not an element of this network
*/
int degree(N node);
/**
* Returns the count of {@code node}'s {@link #inEdges(Object) incoming edges} in a directed
* network. In an undirected network, returns the {@link #degree(Object)}.
*
* <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}.
*
* @throws IllegalArgumentException if {@code node} is not an element of this network
*/
int inDegree(N node);
/**
* Returns the count of {@code node}'s {@link #outEdges(Object) outgoing edges} in a directed
* network. In an undirected network, returns the {@link #degree(Object)}.
*
* <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}.
*
* @throws IllegalArgumentException if {@code node} is not an element of this network
*/
int outDegree(N node);
/**
* Returns the nodes which are the endpoints of {@code edge} in this network.
*
* @throws IllegalArgumentException if {@code edge} is not an element of this network
*/
EndpointPair<N> incidentNodes(E edge);
/**
* Returns the edges which have an {@link #incidentNodes(Object) incident node} in common with
* {@code edge}. An edge is not considered adjacent to itself.
*
* @throws IllegalArgumentException if {@code edge} is not an element of this network
*/
Set<E> adjacentEdges(E edge);
/**
* Returns the set of edges directly connecting {@code nodeU} to {@code nodeV}.
*
* <p>In an undirected network, this is equal to {@code edgesConnecting(nodeV, nodeU)}.
*
* <p>The resulting set of edges will be parallel (i.e. have equal {@link #incidentNodes(Object)}.
* If this network does not {@link #allowsParallelEdges() allow parallel edges}, the resulting set
* will contain at most one edge (equivalent to {@code edgeConnecting(nodeU, nodeV).asSet()}).
*
* @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this
* network
*/
Set<E> edgesConnecting(N nodeU, N nodeV);
/**
* Returns the single edge directly connecting {@code nodeU} to {@code nodeV}, if one is present.
*
* <p>In an undirected network, this is equal to {@code edgeConnecting(nodeV, nodeU)}.
*
* @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU}
* to {@code nodeV}
* @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this
* network
*/
Optional<E> edgeConnecting(N nodeU, N nodeV);
//
// Network identity
//
/**
* Returns {@code true} iff {@code object} is a {@link Network} that has the same elements and the
* same structural relationships as those in this network.
*
* <p>Thus, two networks A and B are equal if <b>all</b> of the following are true:
*
* <ul>
* <li>A and B have equal {@link #isDirected() directedness}.
* <li>A and B have equal {@link #nodes() node sets}.
* <li>A and B have equal {@link #edges() edge sets}.
* <li>Every edge in A and B connects the same nodes in the same direction (if any).
* </ul>
*
* <p>Network properties besides {@link #isDirected() directedness} do <b>not</b> affect equality.
* For example, two networks may be considered equal even if one allows parallel edges and the
* other doesn't. Additionally, the order in which nodes or edges are added to the network, and
* the order in which they are iterated over, are irrelevant.
*
* <p>A reference implementation of this is provided by {@link AbstractNetwork#equals(Object)}.
*/
@Override
boolean equals(@Nullable Object object);
/**
* Returns the hash code for this network. The hash code of a network is defined as the hash code
* of a map from each of its {@link #edges() edges} to their {@link #incidentNodes(Object)
* incident nodes}.
*
* <p>A reference implementation of this is provided by {@link AbstractNetwork#hashCode()}.
*/
@Override
int hashCode();
}