SymbolDigraph.java


Below is the syntax highlighted version of SymbolDigraph.java.


/******************************************************************************
 *  Compilation:  javac SymbolDigraph.java
 *  Execution:    java SymbolDigraph
 *  Dependencies: ST.java Digraph.java In.java
 *  Data files:   http://algs4.cs.princeton.edu/42digraph/routes.txt
 *  
 *  %  java SymbolDigraph routes.txt " "
 *  JFK
 *     MCO
 *     ATL
 *     ORD
 *  ATL
 *     HOU
 *     MCO
 *  LAX
 *
 ******************************************************************************/

package edu.princeton.cs.algs4;

/**
 *  The {@code SymbolDigraph} class represents a digraph, where the
 *  vertex names are arbitrary strings.
 *  By providing mappings between string vertex names and integers,
 *  it serves as a wrapper around the
 *  {@link Digraph} data type, which assumes the vertex names are integers
 *  between 0 and <em>V</em> - 1.
 *  It also supports initializing a symbol digraph from a file.
 *  <p>
 *  This implementation uses an {@link ST} to map from strings to integers,
 *  an array to map from integers to strings, and a {@link Digraph} to store
 *  the underlying graph.
 *  The <em>indexOf</em> and <em>contains</em> operations take time 
 *  proportional to log <em>V</em>, where <em>V</em> is the number of vertices.
 *  The <em>nameOf</em> operation takes constant time.
 *  <p>
 *  For additional documentation, see <a href="http://algs4.cs.princeton.edu/42digraph">Section 4.2</a> of
 *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
 *
 *  @author Robert Sedgewick
 *  @author Kevin Wayne
 */
public class SymbolDigraph {
    private ST<String, Integer> st;  // string -> index
    private String[] keys;           // index  -> string
    private Digraph graph;           // the underlying digraph

    /**  
     * Initializes a digraph from a file using the specified delimiter.
     * Each line in the file contains
     * the name of a vertex, followed by a list of the names
     * of the vertices adjacent to that vertex, separated by the delimiter.
     * @param filename the name of the file
     * @param delimiter the delimiter between fields
     */
    public SymbolDigraph(String filename, String delimiter) {
        st = new ST<String, Integer>();

        // First pass builds the index by reading strings to associate
        // distinct strings with an index
        In in = new In(filename);
        while (in.hasNextLine()) {
            String[] a = in.readLine().split(delimiter);
            for (int i = 0; i < a.length; i++) {
                if (!st.contains(a[i]))
                    st.put(a[i], st.size());
            }
        }

        // inverted index to get string keys in an aray
        keys = new String[st.size()];
        for (String name : st.keys()) {
            keys[st.get(name)] = name;
        }

        // second pass builds the digraph by connecting first vertex on each
        // line to all others
        graph = new Digraph(st.size());
        in = new In(filename);
        while (in.hasNextLine()) {
            String[] a = in.readLine().split(delimiter);
            int v = st.get(a[0]);
            for (int i = 1; i < a.length; i++) {
                int w = st.get(a[i]);
                graph.addEdge(v, w);
            }
        }
    }

    /**
     * Does the digraph contain the vertex named {@code s}?
     * @param s the name of a vertex
     * @return {@code true} if {@code s} is the name of a vertex, and {@code false} otherwise
     */
    public boolean contains(String s) {
        return st.contains(s);
    }

    /**
     * Returns the integer associated with the vertex named {@code s}.
     * @param s the name of a vertex
     * @return the integer (between 0 and <em>V</em> - 1) associated with the vertex named {@code s}
     * @deprecated Replaced by {@link #indexOf(String)}.
     */
    @Deprecated
    public int index(String s) {
        return st.get(s);
    }

    /**
     * Returns the integer associated with the vertex named {@code s}.
     * @param s the name of a vertex
     * @return the integer (between 0 and <em>V</em> - 1) associated with the vertex named {@code s}
     */
    public int indexOf(String s) {
        return st.get(s);
    }

    /**
     * Returns the name of the vertex associated with the integer {@code v}.
     * @param  v the integer corresponding to a vertex (between 0 and <em>V</em> - 1) 
     * @return the name of the vertex associated with the integer {@code v}
     * @throws IllegalArgumentException unless {@code 0 <= v < V}
     * @deprecated Replaced by {@link #nameOf(int)}.
     */
    @Deprecated
    public String name(int v) {
        validateVertex(v);
        return keys[v];
    }

    /**
     * Returns the name of the vertex associated with the integer {@code v}.
     * @param  v the integer corresponding to a vertex (between 0 and <em>V</em> - 1) 
     * @return the name of the vertex associated with the integer {@code v}
     * @throws IllegalArgumentException unless {@code 0 <= v < V}
     */
    public String nameOf(int v) {
        validateVertex(v);
        return keys[v];
    }

    /**
     * Returns the digraph assoicated with the symbol graph. It is the client's responsibility
     * not to mutate the digraph.
     *
     * @return the digraph associated with the symbol digraph
     * @deprecated Replaced by {@link #digraph()}.
     */
    @Deprecated
    public Digraph G() {
        return graph;
    }

    /**
     * Returns the digraph assoicated with the symbol graph. It is the client's responsibility
     * not to mutate the digraph.
     *
     * @return the digraph associated with the symbol digraph
     */
    public Digraph digraph() {
        return graph;
    }

    // throw an IllegalArgumentException unless {@code 0 <= v < V}
    private void validateVertex(int v) {
         int V = graph.V();
        if (v < 0 || v >= V)
            throw new IllegalArgumentException("vertex " + v + " is not between 0 and " + (V-1));
    }

    /**
     * Unit tests the {@code SymbolDigraph} data type.
     *
     * @param args the command-line arguments
     */
    public static void main(String[] args) {
        String filename  = args[0];
        String delimiter = args[1];
        SymbolDigraph sg = new SymbolDigraph(filename, delimiter);
        Digraph graph = sg.digraph();
        while (!StdIn.isEmpty()) {
            String t = StdIn.readLine();
            for (int v : graph.adj(sg.index(t))) {
                StdOut.println("   " + sg.name(v));
            }
        }
    }
}

/******************************************************************************
 *  Copyright 2002-2016, Robert Sedgewick and Kevin Wayne.
 *
 *  This file is part of algs4.jar, which accompanies the textbook
 *
 *      Algorithms, 4th edition by Robert Sedgewick and Kevin Wayne,
 *      Addison-Wesley Professional, 2011, ISBN 0-321-57351-X.
 *      http://algs4.cs.princeton.edu
 *
 *
 *  algs4.jar is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  algs4.jar is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with algs4.jar.  If not, see http://www.gnu.org/licenses.
 ******************************************************************************/


Last updated: Sat Jun 17 06:05:45 EDT 2017.