java实现图（无向图）数据结构

/****************************************************************************** *  Compilation:  javac Graph.java         *  Execution:    java Graph input.txt *  Dependencies: Bag.java In.java StdOut.java *  Data files:   http://algs4.cs.princeton.edu/41graph/tinyG.txt * *  A graph, implemented using an array of sets. *  Parallel edges and self-loops allowed. * *  % java Graph tinyG.txt *  13 vertices, 13 edges  *  0: 6 2 1 5  *  1: 0  *  2: 0  *  3: 5 4  *  4: 5 6 3  *  5: 3 4 0  *  6: 0 4  *  7: 8  *  8: 7  *  9: 11 10 12  *  10: 9  *  11: 9 12  *  12: 11 9  * *  % java Graph mediumG.txt *  250 vertices, 1273 edges  *  0: 225 222 211 209 204 202 191 176 163 160 149 114 97 80 68 59 58 49 44 24 15  *  1: 220 203 200 194 189 164 150 130 107 72  *  2: 141 110 108 86 79 51 42 18 14  *  ... *   ******************************************************************************/package edu.princeton.cs.algs4;/** *  The <tt>Graph</tt> class represents an undirected graph of vertices *  named 0 through <em>V</em> - 1. *  It supports the following two primary operations: add an edge to the graph, *  iterate over all of the vertices adjacent to a vertex. It also provides *  methods for returning the number of vertices <em>V</em> and the number *  of edges <em>E</em>. Parallel edges and self-loops are permitted. *  <p> *  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 vertices adjacent to a given vertex, which takes *  time proportional to the number of such vertices. *  <p> *  For additional documentation, see <a href="http://algs4.cs.princeton.edu/41graph">Section 4.1</a> *  of <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne. * *  @author Robert Sedgewick *  @author Kevin Wayne */public class Graph {    private static final String NEWLINE = System.getProperty("line.separator");    private final int V;    private int E;    private Bag<Integer>[] adj;        /**     * Initializes an empty graph with <tt>V</tt> vertices and 0 edges.     * param V the number of vertices     *     * @param  V number of vertices     * @throws IllegalArgumentException if <tt>V</tt> < 0     */    public Graph(int V) {        if (V < 0) throw new IllegalArgumentException("Number of vertices must be nonnegative");        this.V = V;        this.E = 0;        adj = (Bag<Integer>[]) new Bag[V];        for (int v = 0; v < V; v++) {            adj[v] = new Bag<Integer>();        }    }    /**       * Initializes a graph from an input stream.     * The format is the number of vertices <em>V</em>,     * followed by the number of edges <em>E</em>,     * followed by <em>E</em> pairs of vertices, with each entry separated by whitespace.     *     * @param  in the input stream     * @throws IndexOutOfBoundsException if the endpoints of any edge are not in prescribed range     * @throws IllegalArgumentException if the number of vertices or edges is negative     */    public Graph(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();            addEdge(v, w);        }    }    /**     * Initializes a new graph that is a deep copy of <tt>G</tt>.     *     * @param  G the graph to copy     */    public Graph(Graph G) {        this(G.V());        this.E = G.E();        for (int v = 0; v < G.V(); v++) {            // reverse so that adjacency list is in same order as original            Stack<Integer> reverse = new Stack<Integer>();            for (int w : G.adj[v]) {                reverse.push(w);            }            for (int w : reverse) {                adj[v].add(w);            }        }    }    /**     * Returns the number of vertices in this graph.     *     * @return the number of vertices in this graph     */    public int V() {        return V;    }    /**     * Returns the number of edges in this graph.     *     * @return the number of edges in this graph     */    public int E() {        return E;    }    // throw an IndexOutOfBoundsException unless 0 <= v < V    private void validateVertex(int v) {        if (v < 0 || v >= V)            throw new IndexOutOfBoundsException("vertex " + v + " is not between 0 and " + (V-1));    }    /**     * Adds the undirected edge v-w to this graph.     *     * @param  v one vertex in the edge     * @param  w the other vertex in the edge     * @throws IndexOutOfBoundsException unless both 0 <= v < V and 0 <= w < V     */    public void addEdge(int v, int w) {        validateVertex(v);        validateVertex(w);        E++;        adj[v].add(w);        adj[w].add(v);    }    /**     * Returns the vertices adjacent to vertex <tt>v</tt>.     *     * @param  v the vertex     * @return the vertices adjacent to vertex <tt>v</tt>, as an iterable     * @throws IndexOutOfBoundsException unless 0 <= v < V     */    public Iterable<Integer> adj(int v) {        validateVertex(v);        return adj[v];    }    /**     * Returns the degree of vertex <tt>v</tt>.     *     * @param  v the vertex     * @return the degree of vertex <tt>v</tt>     * @throws IndexOutOfBoundsException unless 0 <= v < V     */    public int degree(int v) {        validateVertex(v);        return adj[v].size();    }    /**     * Returns a string representation of this graph.     *     * @return the number of vertices <em>V</em>, followed by the number of edges <em>E</em>,     *         followed by the <em>V</em> adjacency lists     */    public String toString() {        StringBuilder s = new StringBuilder();        s.append(V + " vertices, " + E + " edges " + NEWLINE);        for (int v = 0; v < V; v++) {            s.append(v + ": ");            for (int w : adj[v]) {                s.append(w + " ");            }            s.append(NEWLINE);        }        return s.toString();    }    /**     * Unit tests the <tt>Graph</tt> data type.     */    public static void main(String[] args) {        In in = new In(args[0]);        Graph G = new Graph(in);        StdOut.println(G);    }}