189 lines
6.6 KiB
Java
189 lines
6.6 KiB
Java
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import edu.princeton.cs.introcs.In;
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import edu.princeton.cs.introcs.StdOut;
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import edu.princeton.cs.introcs.StdRandom;
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/*************************************************************************
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* Compilation: javac FlowNetwork.java
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* Execution: java FlowNetwork V E
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* Dependencies: Bag.java FlowEdge.java
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*
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* A capacitated flow network, implemented using adjacency lists.
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*
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*************************************************************************/
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/**
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* The FlowNetwork class represents a capacitated network
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* with vertices named 0 through V - 1, where each directed
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* edge is of type {@link FlowEdge} and has a real-valued capacity
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* and flow.
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* It supports the following two primary operations: add an edge to the network,
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* iterate over all of the edges incident to or from a vertex. It also provides
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* methods for returning the number of vertices V and the number
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* of edges E . Parallel edges and self-loops are permitted.
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*
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* This implementation uses an adjacency-lists representation, which
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* is a vertex-indexed array of @link{Bag} objects.
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* All operations take constant time (in the worst case) except
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* iterating over the edges incident to a given vertex, which takes
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* time proportional to the number of such edges.
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*
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* For additional documentation,
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* see <a href="http://algs4.cs.princeton.edu/64maxflow">Section 6.4</a> of
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* Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.
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*
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* @author Robert Sedgewick
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* @author Kevin Wayne
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*/
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public class FlowNetwork {
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private final int V;
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private int E;
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private Bag<FlowEdge>[] adj;
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/**
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* Initializes an empty flow network with V vertices and 0 edges.
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* param V the number of vertices
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* @throws java.lang.IllegalArgumentException if V < 0
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*/
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public FlowNetwork(int V) {
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if (V < 0) throw new IllegalArgumentException("Number of vertices in a Graph must be nonnegative");
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this.V = V;
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this.E = 0;
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adj = (Bag<FlowEdge>[]) new Bag[V];
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for (int v = 0; v < V; v++)
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adj[v] = new Bag<FlowEdge>();
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}
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/**
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* Initializes a random flow network with V vertices and E edges.
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* The capacities are integers between 0 and 99 and the flow values are zero.
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* param V the number of vertices
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* param E the number of edges
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* @throws java.lang.IllegalArgumentException if V < 0
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* @throws java.lang.IllegalArgumentException if E < 0
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*/
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public FlowNetwork(int V, int E) {
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this(V);
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if (E < 0) throw new IllegalArgumentException("Number of edges must be nonnegative");
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for (int i = 0; i < E; i++) {
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int v = StdRandom.uniform(V);
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int w = StdRandom.uniform(V);
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double capacity = StdRandom.uniform(100);
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addEdge(new FlowEdge(v, w, capacity));
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}
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}
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/**
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* Initializes a flow network from an input stream.
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* The format is the number of vertices V ,
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* followed by the number of edges E ,
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* followed by E pairs of vertices and edge capacities,
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* with each entry separated by whitespace.
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* @param in the input stream
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* @throws java.lang.IndexOutOfBoundsException if the endpoints of any edge are not in prescribed range
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* @throws java.lang.IllegalArgumentException if the number of vertices or edges is negative
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*/
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public FlowNetwork(In in) {
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this(in.readInt());
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int E = in.readInt();
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if (E < 0) throw new IllegalArgumentException("Number of edges must be nonnegative");
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for (int i = 0; i < E; i++) {
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int v = in.readInt();
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int w = in.readInt();
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if (v < 0 || v >= V) throw new IndexOutOfBoundsException("vertex " + v + " is not between 0 and " + (V-1));
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if (w < 0 || w >= V) throw new IndexOutOfBoundsException("vertex " + w + " is not between 0 and " + (V-1));
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double capacity = in.readDouble();
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addEdge(new FlowEdge(v, w, capacity));
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}
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}
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/**
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* Returns the number of vertices in the edge-weighted graph.
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* @return the number of vertices in the edge-weighted graph
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*/
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public int V() {
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return V;
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}
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/**
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* Returns the number of edges in the edge-weighted graph.
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* @return the number of edges in the edge-weighted graph
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*/
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public int E() {
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return E;
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}
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/**
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* Adds the edge e to the network.
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* @param e the edge
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* @throws java.lang.IndexOutOfBoundsException unless endpoints of edge are between 0 and V-1
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*/
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public void addEdge(FlowEdge e) {
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int v = e.from();
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int w = e.to();
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if (v < 0 || v >= V) throw new IndexOutOfBoundsException("vertex " + v + " is not between 0 and " + (V-1));
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if (w < 0 || w >= V) throw new IndexOutOfBoundsException("vertex " + w + " is not between 0 and " + (V-1));
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adj[v].add(e);
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adj[w].add(e);
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E++;
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}
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/**
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* Returns the edges incident on vertex v (includes both edges pointing to
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* and from v ).
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* @return the edges incident on vertex v as an Iterable
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* @param v the vertex
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* @throws java.lang.IndexOutOfBoundsException unless 0 <= v < V
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*/
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public Iterable<FlowEdge> adj(int v) {
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if (v < 0 || v >= V) throw new IndexOutOfBoundsException("vertex " + v + " is not between 0 and " + (V-1));
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return adj[v];
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}
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// return list of all edges - excludes self loops
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public Iterable<FlowEdge> edges() {
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Bag<FlowEdge> list = new Bag<FlowEdge>();
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for (int v = 0; v < V; v++)
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for (FlowEdge e : adj(v)) {
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if (e.to() != v)
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list.add(e);
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}
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return list;
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}
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/**
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* Returns a string representation of the flow network.
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* This method takes time proportional to E + V .
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* @return the number of vertices V , followed by the number of edges E ,
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* followed by the V adjacency lists
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*/
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@Override
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public String toString() {
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String NEWLINE = System.getProperty("line.separator");
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StringBuilder s = new StringBuilder();
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s.append(V + " " + E + NEWLINE);
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for (int v = 0; v < V; v++) {
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s.append(v + ": ");
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for (FlowEdge e : adj[v]) {
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if (e.to() != v) s.append(e + " ");
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}
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s.append(NEWLINE);
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}
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return s.toString();
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}
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/**
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* Unit tests the FlowNetwork data type.
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*/
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public static void main(String[] args) {
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In in = new In(args[0]);
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FlowNetwork G = new FlowNetwork(in);
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StdOut.println(G);
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}
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}
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