LookupIndex.java

Below is the syntax highlighted version of LookupIndex.java from §3.5 Searching Applications.

/******************************************************************************
 *  Compilation:  javac LookupIndex.java
 *  Execution:    java LookupIndex movies.txt "/"
 *  Dependencies: ST.java Queue.java In.java StdIn.java StdOut.java
 *  Data files:   https://algs4.cs.princeton.edu/35applications/aminoI.csv
 *                https://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
 *    ...
 *
 ******************************************************************************/

/**
 *  The {@code LookupIndex} class provides a data-driven client for reading in a
 *  key-value pairs from a file; then, printing the values corresponding to the
 *  keys found on standard input. Keys are strings; values are lists of strings.
 *  The separating delimiter is taken as a command-line argument. This client
 *  is sometimes known as an <em>inverted index</em>.
 *  <p>
 *  For additional documentation, see <a href="https://algs4.cs.princeton.edu/35applications">Section 3.5</a> of
 *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
 *
 *  @author Robert Sedgewick
 *  @author Kevin Wayne
 */
public class LookupIndex {

    // Do not instantiate.
    private LookupIndex() { }

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

        ST<String, Queue<String>> st = new ST<String, Queue<String>>();
        ST<String, Queue<String>> ts = new ST<String, Queue<String>>();

        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<String>());
                if (!ts.contains(val)) ts.put(val, new Queue<String>());
                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);
        }

    }

}