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Code examples from Princeton's "Algorithms" textbook, 4th Edition.

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package edu.princeton.cs.algorithms;

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

/*************************************************************************
 *  Compilation:  javac LookupIndex.java
 *  Execution:    java LookupIndex movies.txt "/"
 *  Dependencies: ST.java Queue.java In.java StdIn.java StdOut.java
 *  Data files:   http://algs4.cs.princeton.edu/35applications/aminoI.csv
 *                http://algs4.cs.princeton.edu/35applications/movies.txt
 *
 *  % java LookupIndex aminoI.csv ","
 *  Serine
 *    TCT
 *    TCA
 *    TCG
 *    AGT
 *    AGC
 *  TCG
 *    Serine
 *
 *  % java LookupIndex movies.txt "/"
 *  Bacon, Kevin
 *    Animal House (1978)
 *    Apollo 13 (1995)
 *    Beauty Shop (2005)
 *    Diner (1982)
 *    Few Good Men, A (1992)
 *    Flatliners (1990)
 *    Footloose (1984)
 *    Friday the 13th (1980)
 *    ...
 *  Tin Men (1987)
 *    DeBoy, David
 *    Blumenfeld, Alan
 *    ...
 *
 *************************************************************************/

public class LookupIndex { 

    public static void main(String[] args) {
        String filename  = args[0];
        String separator = args[1];
        In in = new In(filename);

        ST> st = new ST>();
        ST> ts = new ST>();

        while (in.hasNextLine()) {
            String line = in.readLine();
            String[] fields = line.split(separator);
            String key = fields[0];
            for (int i = 1; i < fields.length; i++) {
                String val = fields[i];
                if (!st.contains(key)) st.put(key, new Queue());
                if (!ts.contains(val)) ts.put(val, new Queue());
                st.get(key).enqueue(val);
                ts.get(val).enqueue(key);
            }
        }

        StdOut.println("Done indexing");

        // read queries from standard input, one per line
        while (!StdIn.isEmpty()) {
            String query = StdIn.readLine();
            if (st.contains(query)) 
                for (String vals : st.get(query))
                    StdOut.println("  " + vals);
            if (ts.contains(query)) 
                for (String keys : ts.get(query))
                    StdOut.println("  " + keys);
        }

    }

}