edu.princeton.cs.algs4.FlowNetwork Maven / Gradle / Ivy
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/******************************************************************************
* Compilation: javac FlowNetwork.java
* Execution: java FlowNetwork V E
* Dependencies: Bag.java FlowEdge.java
*
* A capacitated flow network, implemented using adjacency lists.
*
******************************************************************************/
package edu.princeton.cs.algs4;
/**
* The {@code FlowNetwork} class represents a capacitated network
* with vertices named 0 through V - 1, where each directed
* edge is of type {@link FlowEdge} and has a real-valued capacity
* and flow.
* It supports the following two primary operations: add an edge to the network,
* iterate over all of the edges incident to or from a vertex. It also provides
* methods for returning the number of vertices V and the number
* of edges E. Parallel edges and self-loops are permitted.
*
* This implementation uses an adjacency-lists representation, which
* is a vertex-indexed array of {@link Bag} objects.
* All operations take constant time (in the worst case) except
* iterating over the edges incident to a given vertex, which takes
* time proportional to the number of such edges.
*
* For additional documentation,
* see Section 6.4 of
* Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class FlowNetwork {
private static final String NEWLINE = System.getProperty("line.separator");
private final int V;
private int E;
private Bag[] adj;
/**
* Initializes an empty flow network with {@code V} vertices and 0 edges.
* @param V the number of vertices
* @throws IllegalArgumentException if {@code V < 0}
*/
public FlowNetwork(int V) {
if (V < 0) throw new IllegalArgumentException("Number of vertices in a Graph must be nonnegative");
this.V = V;
this.E = 0;
adj = (Bag[]) new Bag[V];
for (int v = 0; v < V; v++)
adj[v] = new Bag();
}
/**
* Initializes a random flow network with {@code V} vertices and E edges.
* The capacities are integers between 0 and 99 and the flow values are zero.
* @param V the number of vertices
* @param E the number of edges
* @throws IllegalArgumentException if {@code V < 0}
* @throws IllegalArgumentException if {@code E < 0}
*/
public FlowNetwork(int V, int E) {
this(V);
if (E < 0) throw new IllegalArgumentException("Number of edges must be nonnegative");
for (int i = 0; i < E; i++) {
int v = StdRandom.uniform(V);
int w = StdRandom.uniform(V);
double capacity = StdRandom.uniform(100);
addEdge(new FlowEdge(v, w, capacity));
}
}
/**
* Initializes a flow network from an input stream.
* The format is the number of vertices V,
* followed by the number of edges E,
* followed by E pairs of vertices and edge capacities,
* with each entry separated by whitespace.
* @param in the input stream
* @throws IllegalArgumentException if the endpoints of any edge are not in prescribed range
* @throws IllegalArgumentException if the number of vertices or edges is negative
*/
public FlowNetwork(In in) {
this(in.readInt());
int E = in.readInt();
if (E < 0) throw new IllegalArgumentException("number of edges must be nonnegative");
for (int i = 0; i < E; i++) {
int v = in.readInt();
int w = in.readInt();
validateVertex(v);
validateVertex(w);
double capacity = in.readDouble();
addEdge(new FlowEdge(v, w, capacity));
}
}
/**
* Returns the number of vertices in the edge-weighted graph.
* @return the number of vertices in the edge-weighted graph
*/
public int V() {
return V;
}
/**
* Returns the number of edges in the edge-weighted graph.
* @return the number of edges in the edge-weighted graph
*/
public int E() {
return E;
}
// throw an IllegalArgumentException unless {@code 0 <= v < V}
private void validateVertex(int v) {
if (v < 0 || v >= V)
throw new IllegalArgumentException("vertex " + v + " is not between 0 and " + (V-1));
}
/**
* Adds the edge {@code e} to the network.
* @param e the edge
* @throws IllegalArgumentException unless endpoints of edge are between
* {@code 0} and {@code V-1}
*/
public void addEdge(FlowEdge e) {
int v = e.from();
int w = e.to();
validateVertex(v);
validateVertex(w);
adj[v].add(e);
adj[w].add(e);
E++;
}
/**
* Returns the edges incident on vertex {@code v} (includes both edges pointing to
* and from {@code v}).
* @param v the vertex
* @return the edges incident on vertex {@code v} as an Iterable
* @throws IllegalArgumentException unless {@code 0 <= v < V}
*/
public Iterable adj(int v) {
validateVertex(v);
return adj[v];
}
// return list of all edges - excludes self loops
public Iterable edges() {
Bag list = new Bag();
for (int v = 0; v < V; v++)
for (FlowEdge e : adj(v)) {
if (e.to() != v)
list.add(e);
}
return list;
}
/**
* Returns a string representation of the flow network.
* This method takes time proportional to E + V.
* @return the number of vertices V, followed by the number of edges E,
* followed by the V adjacency lists
*/
public String toString() {
StringBuilder s = new StringBuilder();
s.append(V + " " + E + NEWLINE);
for (int v = 0; v < V; v++) {
s.append(v + ": ");
for (FlowEdge e : adj[v]) {
if (e.to() != v) s.append(e + " ");
}
s.append(NEWLINE);
}
return s.toString();
}
/**
* Unit tests the {@code FlowNetwork} data type.
*
* @param args the command-line arguments
*/
public static void main(String[] args) {
In in = new In(args[0]);
FlowNetwork G = new FlowNetwork(in);
StdOut.println(G);
}
}
/******************************************************************************
* Copyright 2002-2018, Robert Sedgewick and Kevin Wayne.
*
* This file is part of algs4.jar, which accompanies the textbook
*
* Algorithms, 4th edition by Robert Sedgewick and Kevin Wayne,
* Addison-Wesley Professional, 2011, ISBN 0-321-57351-X.
* http://algs4.cs.princeton.edu
*
*
* algs4.jar is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* algs4.jar is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with algs4.jar. If not, see http://www.gnu.org/licenses.
******************************************************************************/