MoveToFront.java

import edu.princeton.cs.algs4.BinaryStdIn;
import edu.princeton.cs.algs4.BinaryStdOut;
import java.util.Arrays;

public class MoveToFront {
    // apply move-to-front encoding, reading from standard input and writing to standard output
    public static void encode() {
        char[] seq = initializeASCII();
        while (!BinaryStdIn.isEmpty()) { // read each 8-bit character c from standard input, one at a time
            char c = BinaryStdIn.readChar();
            int b = String.copyValueOf(seq).indexOf(c);
            BinaryStdOut.write((byte) b);
            seq = shiftToFront(seq, b);
        }
        BinaryStdOut.close();
    }

    // apply move-to-front decoding, reading from standard input and writing to standard output
    public static void decode() {
        char[] seq = initializeASCII();
        while (!BinaryStdIn.isEmpty()) { // read each 8-bit character c from standard input, one at a time
            byte b = BinaryStdIn.readByte();
            char c = (char) (b & 0xff);
            BinaryStdOut.write(seq[c]);
            seq = shiftToFront(seq, c);
        }
        BinaryStdOut.close();
    }

    // ------------- UTILITIES ----------------//

    private static char[] initializeASCII() {
        int r = 256; // extended ASCII
        char[] seq = new char[r];
        for (int i = 0; i < r; i++) { // Initialization of the ordered sequence of 256 extended ASCII characters
            seq[i] = (char) (i & 0xff);
        }
        return seq;
    }

    private static char[] shiftToFront(char[] seq, int idx) {
        int n = seq.length;
        char[] copy = Arrays.copyOf(seq, n);
        char c = seq[idx];
        char[] dest = new char[n];
        System.arraycopy(copy, 0, dest, 1, idx);
        System.arraycopy(copy, idx + 1, dest, idx + 1, n - idx - 1);
        dest[0] = c;
        seq = dest;
        return seq;
    }

    // if args[0] is "-", apply move-to-front encoding
    // if args[0] is "+", apply move-to-front decoding
    public static void main(String[] args) {
        if (args[0].equals("-")) encode();
        else if (args[0].equals("+")) decode();
        else throw new IllegalArgumentException("Illegal command line argument");
    }
}