229 lines
8.0 KiB
Java
229 lines
8.0 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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/*************************************************************************
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* Compilation: javac EdgeWeightedGraph.java
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* Execution: java EdgeWeightedGraph filename.txt
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* Dependencies: Bag.java Edge.java In.java StdOut.java
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* Data files: http://algs4.cs.princeton.edu/43mst/tinyEWG.txt
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*
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* An edge-weighted undirected graph, implemented using adjacency lists.
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* Parallel edges and self-loops are permitted.
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*
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* % java EdgeWeightedGraph tinyEWG.txt
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* 8 16
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* 0: 6-0 0.58000 0-2 0.26000 0-4 0.38000 0-7 0.16000
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* 1: 1-3 0.29000 1-2 0.36000 1-7 0.19000 1-5 0.32000
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* 2: 6-2 0.40000 2-7 0.34000 1-2 0.36000 0-2 0.26000 2-3 0.17000
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* 3: 3-6 0.52000 1-3 0.29000 2-3 0.17000
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* 4: 6-4 0.93000 0-4 0.38000 4-7 0.37000 4-5 0.35000
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* 5: 1-5 0.32000 5-7 0.28000 4-5 0.35000
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* 6: 6-4 0.93000 6-0 0.58000 3-6 0.52000 6-2 0.40000
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* 7: 2-7 0.34000 1-7 0.19000 0-7 0.16000 5-7 0.28000 4-7 0.37000
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*
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*************************************************************************/
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/**
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* The EdgeWeightedGraph class represents an edge-weighted
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* graph of vertices named 0 through V - 1, where each
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* undirected edge is of type {@link Edge} and has a real-valued weight.
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* It supports the following two primary operations: add an edge to the graph,
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* iterate over all of the edges incident to 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/43mst">Section 4.3</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 EdgeWeightedGraph {
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private final int V;
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private int E;
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private Bag<Edge>[] adj;
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/**
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* Initializes an empty edge-weighted graph 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 EdgeWeightedGraph(int V) {
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if (V < 0) throw new IllegalArgumentException("Number of vertices must be nonnegative");
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this.V = V;
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this.E = 0;
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adj = (Bag<Edge>[]) new Bag[V];
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for (int v = 0; v < V; v++) {
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adj[v] = new Bag<Edge>();
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}
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}
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/**
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* Initializes a random edge-weighted graph with V vertices and E edges.
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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 EdgeWeightedGraph(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 = (int) (Math.random() * V);
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int w = (int) (Math.random() * V);
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double weight = Math.round(100 * Math.random()) / 100.0;
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Edge e = new Edge(v, w, weight);
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addEdge(e);
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}
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}
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/**
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* Initializes an edge-weighted graph 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 weights,
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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 EdgeWeightedGraph(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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double weight = in.readDouble();
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Edge e = new Edge(v, w, weight);
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addEdge(e);
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}
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}
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/**
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* Initializes a new edge-weighted graph that is a deep copy of G .
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* @param G the edge-weighted graph to copy
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*/
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public EdgeWeightedGraph(EdgeWeightedGraph G) {
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this(G.V());
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this.E = G.E();
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for (int v = 0; v < G.V(); v++) {
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// reverse so that adjacency list is in same order as original
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Stack<Edge> reverse = new Stack<Edge>();
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for (Edge e : G.adj[v]) {
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reverse.push(e);
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}
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for (Edge e : reverse) {
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adj[v].add(e);
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}
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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 undirected edge e to the edge-weighted graph.
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* @param e the edge
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* @throws java.lang.IndexOutOfBoundsException unless both endpoints are between 0 and V-1
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*/
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public void addEdge(Edge e) {
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int v = e.either();
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int w = e.other(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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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 .
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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<Edge> 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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/**
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* Returns all edges in the edge-weighted graph.
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* To iterate over the edges in the edge-weighted graph, use foreach notation:
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* for (Edge e : G.edges()) .
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* @return all edges in the edge-weighted graph as an Iterable.
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*/
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public Iterable<Edge> edges() {
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Bag<Edge> list = new Bag<Edge>();
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for (int v = 0; v < V; v++) {
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int selfLoops = 0;
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for (Edge e : adj(v)) {
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if (e.other(v) > v) {
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list.add(e);
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}
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// only add one copy of each self loop (self loops will be consecutive)
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else if (e.other(v) == v) {
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if (selfLoops % 2 == 0) list.add(e);
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selfLoops++;
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}
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}
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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 edge-weighted graph.
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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 of edges
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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 (Edge e : adj[v]) {
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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 EdgeWeightedGraph 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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EdgeWeightedGraph G = new EdgeWeightedGraph(in);
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StdOut.println(G);
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}
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}
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