edu.princeton.cs.algorithms.FlowNetwork Maven / Gradle / Ivy
Show all versions of algorithms Show documentation
package edu.princeton.cs.algorithms;
import edu.princeton.cs.introcs.In;
import edu.princeton.cs.introcs.StdOut;
import edu.princeton.cs.introcs.StdRandom;
/*************************************************************************
* Compilation: javac FlowNetwork.java
* Execution: java FlowNetwork V E
* Dependencies: Bag.java FlowEdge.java
*
* A capacitated flow network, implemented using adjacency lists.
*
*************************************************************************/
/**
* The 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 final int V;
private int E;
private Bag[] adj;
/**
* Initializes an empty flow network with V vertices and 0 edges.
* param V the number of vertices
* @throws java.lang.IllegalArgumentException if 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 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 java.lang.IllegalArgumentException if V < 0
* @throws java.lang.IllegalArgumentException if 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 java.lang.IndexOutOfBoundsException if the endpoints of any edge are not in prescribed range
* @throws java.lang.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();
if (v < 0 || v >= V) throw new IndexOutOfBoundsException("vertex " + v + " is not between 0 and " + (V-1));
if (w < 0 || w >= V) throw new IndexOutOfBoundsException("vertex " + w + " is not between 0 and " + (V-1));
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;
}
/**
* Adds the edge e to the network.
* @param e the edge
* @throws java.lang.IndexOutOfBoundsException unless endpoints of edge are between 0 and V-1
*/
public void addEdge(FlowEdge e) {
int v = e.from();
int w = e.to();
if (v < 0 || v >= V) throw new IndexOutOfBoundsException("vertex " + v + " is not between 0 and " + (V-1));
if (w < 0 || w >= V) throw new IndexOutOfBoundsException("vertex " + w + " is not between 0 and " + (V-1));
adj[v].add(e);
adj[w].add(e);
E++;
}
/**
* Returns the edges incident on vertex v (includes both edges pointing to
* and from v).
* @return the edges incident on vertex v as an Iterable
* @param v the vertex
* @throws java.lang.IndexOutOfBoundsException unless 0 <= v < V
*/
public Iterable adj(int v) {
if (v < 0 || v >= V) throw new IndexOutOfBoundsException("vertex " + v + " is not between 0 and " + (V-1));
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
*/
@Override
public String toString() {
String NEWLINE = System.getProperty("line.separator");
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 FlowNetwork data type.
*/
public static void main(String[] args) {
In in = new In(args[0]);
FlowNetwork G = new FlowNetwork(in);
StdOut.println(G);
}
}