programming-examples/java/Data_Structures/SymbolDigraph.java

 

import edu.princeton.cs.introcs.In;
import edu.princeton.cs.introcs.StdIn;
import edu.princeton.cs.introcs.StdOut;

/*************************************************************************
 *  Compilation:  javac SymbolDigraph.java
 *  Execution:    java SymbolDigraph
 *  Dependencies: ST.java Digraph.java In.java
 *  
 *  %  java SymbolDigraph routes.txt " "
 *  JFK
 *     MCO
 *     ATL
 *     ORD
 *  ATL
 *     HOU
 *     MCO
 *  LAX
 *
 *************************************************************************/

/**
 *  The  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  V  - 1.
 *  It also supports initializing a symbol digraph from a file.
 *   
 *  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  index  and  contains  operations take time 
 *  proportional to log  V , where  V  is the number of vertices.
 *  The  name  operation takes constant time.
 *   
 *  For additional documentation, see <a href="http://algs4.cs.princeton.edu/42digraph">Section 4.2</a> of
 *   Algorithms, 4th Edition  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 G;

    /**  
     * 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
        G = 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]);
                G.addEdge(v, w);
            }
        }
    }

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

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

    /**
     * Returns the name of the vertex associated with the integer  v .
     * @param v the integer corresponding to a vertex (between 0 and  V  - 1) 
     * @return the name of the vertex associated with the integer  v 
     */
    public String name(int 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
     */
    public Digraph G() {
        return G;
    }


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