RunLength.java
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/******************************************************************************
* Compilation: javac RunLength.java
* Execution: java RunLength - < input.txt (compress)
* Execution: java RunLength + < input.txt (expand)
* Dependencies: BinaryIn.java BinaryOut.java
* Data files: http://algs4.cs.princeton.edu/55compression/4runs.bin
* http://algs4.cs.princeton.edu/55compression/q32x48.bin
* http://algs4.cs.princeton.edu/55compression/q64x96.bin
*
* Compress or expand binary input from standard input using
* run-length encoding.
*
* % java BinaryDump 40 < 4runs.bin
* 0000000000000001111111000000011111111111
* 40 bits
*
* This has runs of 15 0s, 7 1s, 7 0s, and 11 1s.
*
* % java RunLength - < 4runs.bin | java HexDump
* 0f 07 07 0b
* 4 bytes
*
******************************************************************************/
package edu.princeton.cs.algs4;
/**
* The {@code RunLength} class provides static methods for compressing
* and expanding a binary input using run-length coding with 8-bit
* run lengths.
* <p>
* For additional documentation,
* see <a href="http://algs4.cs.princeton.edu/55compress">Section 5.5</a> of
* <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class RunLength {
private static final int R = 256;
private static final int LG_R = 8;
// Do not instantiate.
private RunLength() { }
/**
* Reads a sequence of bits from standard input (that are encoded
* using run-length encoding with 8-bit run lengths); decodes them;
* and writes the results to standard output.
*/
public static void expand() {
boolean b = false;
while (!BinaryStdIn.isEmpty()) {
int run = BinaryStdIn.readInt(LG_R);
for (int i = 0; i < run; i++)
BinaryStdOut.write(b);
b = !b;
}
BinaryStdOut.close();
}
/**
* Reads a sequence of bits from standard input; compresses
* them using run-length coding with 8-bit run lengths; and writes the
* results to standard output.
*/
public static void compress() {
char run = 0;
boolean old = false;
while (!BinaryStdIn.isEmpty()) {
boolean b = BinaryStdIn.readBoolean();
if (b != old) {
BinaryStdOut.write(run, LG_R);
run = 1;
old = !old;
}
else {
if (run == R-1) {
BinaryStdOut.write(run, LG_R);
run = 0;
BinaryStdOut.write(run, LG_R);
}
run++;
}
}
BinaryStdOut.write(run, LG_R);
BinaryStdOut.close();
}
/**
* Sample client that calls {@code compress()} if the command-line
* argument is "-" an {@code expand()} if it is "+".
*
* @param args the command-line arguments
*/
public static void main(String[] args) {
if (args[0].equals("-")) compress();
else if (args[0].equals("+")) expand();
else throw new IllegalArgumentException("Illegal command line argument");
}
}
/******************************************************************************
* 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.
******************************************************************************/