package network;

/******************************************************************************

 *  Compilation:  javac Graph.java        

 *  Execution:    java Graph input.txt

 *  Dependencies: Bag.java Stack.java In.java StdOut.java

 *  Data files:   https://algs4.cs.princeton.edu/41graph/tinyG.txt

 *                https://algs4.cs.princeton.edu/41graph/mediumG.txt

 *                https://algs4.cs.princeton.edu/41graph/largeG.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 

 *  ...

 *  

 ******************************************************************************/

import java.util.NoSuchElementException;

import java.util.Stack;

/**

 *  The {@code Graph} 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.

 *  By convention, a self-loop <em>v</em>-<em>v</em> appears in the

 *  adjacency list of <em>v</em> twice and contributes two to the degree

 *  of <em>v</em>.

 *  <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="https://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 {@code V} vertices and 0 edges.

     * param V the number of vertices

     *

     * @param  V number of vertices

     * @throws IllegalArgumentException if {@code V < 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 the specified 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 IllegalArgumentException if the endpoints of any edge are not in prescribed range

     * @throws IllegalArgumentException if the number of vertices or edges is negative

     * @throws IllegalArgumentException if the input stream is in the wrong format

     */

    public Graph(In in) {

        try {

            this.V = in.readInt();

            if (V < 0) throw new IllegalArgumentException("number of vertices in a Graph must be nonnegative");

            adj = (Bag<Integer>[]) new Bag[V];

            for (int v = 0; v < V; v++) {

                adj[v] = new Bag<Integer>();

            }

            int E = in.readInt();

            if (E < 0) throw new IllegalArgumentException("number of edges in a Graph must be nonnegative");

            for (int i = 0; i < E; i++) {

                int v = in.readInt();

                int w = in.readInt();

                validateVertex(v);

                validateVertex(w);

                addEdge(v, w); 

            }

        }

        catch (NoSuchElementException e) {

            throw new IllegalArgumentException("invalid input format in Graph constructor", e);

        }

    }

    /**

     * Initializes a new graph that is a deep copy of {@code G}.

     *

     * @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 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 undirected edge v-w to this graph.

     *

     * @param  v one vertex in the edge

     * @param  w the other vertex in the edge

     * @throws IllegalArgumentException unless both {@code 0 <= v < V} and {@code 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 {@code v}.

     *

     * @param  v the vertex

     * @return the vertices adjacent to vertex {@code v}, as an iterable

     * @throws IllegalArgumentException unless {@code 0 <= v < V}

     */

    public Iterable<Integer> adj(int v) {

        validateVertex(v);

        return adj[v];

    }

    /**

     * Returns the degree of vertex {@code v}.

     *

     * @param  v the vertex

     * @return the degree of vertex {@code v}

     * @throws IllegalArgumentException unless {@code 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 {@code Graph} data type.

     *

     * @param args the command-line arguments

     */

    public static void main(String[] args) {

        In in = new In(args[0]);

        Graph G = new Graph(in);

        StdOut.println(G);

    }

}