edu.princeton.cs.algs4.Multiway Maven / Gradle / Ivy
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/******************************************************************************
* Compilation: javac Multiway.java
* Execution: java Multiway input1.txt input2.txt input3.txt ...
* Dependencies: IndexMinPQ.java In.java StdOut.java
* Data files: https://algs4.cs.princeton.edu/24pq/m1.txt
* https://algs4.cs.princeton.edu/24pq/m2.txt
* https://algs4.cs.princeton.edu/24pq/m3.txt
*
* Merges together the sorted input stream given as command-line arguments
* into a single sorted output stream on standard output.
*
* % more m1.txt
* A B C F G I I Z
*
* % more m2.txt
* B D H P Q Q
*
* % more m3.txt
* A B E F J N
*
* % java Multiway m1.txt m2.txt m3.txt
* A A B B B C D E F F G H I I J N P Q Q Z
*
******************************************************************************/
package edu.princeton.cs.algs4;
/**
* The {@code Multiway} class provides a client for reading in several
* sorted text files and merging them together into a single sorted
* text stream.
* This implementation uses a {@link IndexMinPQ} to perform the multiway
* merge.
*
* For additional documentation, see Section 2.4
* of Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class Multiway {
// This class should not be instantiated.
private Multiway() { }
// merge together the sorted input streams and write the sorted result to standard output
private static void merge(In[] streams) {
int n = streams.length;
IndexMinPQ pq = new IndexMinPQ(n);
for (int i = 0; i < n; i++)
if (!streams[i].isEmpty())
pq.insert(i, streams[i].readString());
// Extract and print min and read next from its stream.
while (!pq.isEmpty()) {
StdOut.print(pq.minKey() + " ");
int i = pq.delMin();
if (!streams[i].isEmpty())
pq.insert(i, streams[i].readString());
}
StdOut.println();
}
/**
* Reads sorted text files specified as command-line arguments;
* merges them together into a sorted output; and writes
* the results to standard output.
* Note: this client does not check that the input files are sorted.
*
* @param args the command-line arguments
*/
public static void main(String[] args) {
int n = args.length;
In[] streams = new In[n];
for (int i = 0; i < n; i++)
streams[i] = new In(args[i]);
merge(streams);
}
}
/******************************************************************************
* Copyright 2002-2018, 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.
******************************************************************************/