package edu.princeton.cs.algs4.ch55;
import edu.princeton.cs.algs4.ch24.MinPQ;
import edu.princeton.cs.introcs.*;
/*************************************************************************
* Compilation: javac Huffman.java
* Execution: java Huffman - < input.txt (compress)
* Execution: java Huffman + < input.txt (expand)
* Dependencies: BinaryIn.java BinaryOut.java
* Data files: http://algs4.cs.princeton.edu/55compression/abra.txt
* http://algs4.cs.princeton.edu/55compression/tinytinyTale.txt
*
* Compress or expand a binary input stream using the Huffman algorithm.
*
* % java Huffman - < abra.txt | java BinaryDump 60
* 010100000100101000100010010000110100001101010100101010000100
* 000000000000000000000000000110001111100101101000111110010100
* 120 bits
*
* % java Huffman - < abra.txt | java Huffman +
* ABRACADABRA!
*
*************************************************************************/
public class Huffman {
// alphabet size of extended ASCII
private static final int R = 256;
// Huffman trie node
private static class Node implements Comparable<Node> {
private final char ch;
private final int freq;
private final Node left, right;
Node(char ch, int freq, Node left, Node right) {
this.ch = ch;
this.freq = freq;
this.left = left;
this.right = right;
}
// is the node a leaf node?
private boolean isLeaf() {
assert (left == null && right == null) || (left != null && right != null);
return (left == null && right == null);
}
// compare, based on frequency
public int compareTo(Node that) {
return this.freq - that.freq;
}
}
// compress bytes from standard input and write to standard output
public static void compress() {
// read the input
String s = BinaryStdIn.readString();
char[] input = s.toCharArray();
// tabulate frequency counts
int[] freq = new int[R];
for (int i = 0; i < input.length; i++)
freq[input[i]]++;
// build Huffman trie
Node root = buildTrie(freq);
// build code table
String[] st = new String[R];
buildCode(st, root, "");
// print trie for decoder
writeTrie(root);
// print number of bytes in original uncompressed message
BinaryStdOut.write(input.length);
// use Huffman code to encode input
for (int i = 0; i < input.length; i++) {
String code = st[input[i]];
for (int j = 0; j < code.length(); j++) {
if (code.charAt(j) == '0') {
BinaryStdOut.write(false);
}
else if (code.charAt(j) == '1') {
BinaryStdOut.write(true);
}
else throw new IllegalStateException("Illegal state");
}
}
// close output stream
BinaryStdOut.close();
}
// build the Huffman trie given frequencies
private static Node buildTrie(int[] freq) {
// initialze priority queue with singleton trees
MinPQ<Node> pq = new MinPQ<Node>();
for (char i = 0; i < R; i++)
if (freq[i] > 0)
pq.insert(new Node(i, freq[i], null, null));
// special case in case there is only one character with a nonzero frequency
if (pq.size() == 1) {
if (freq['\0'] == 0) pq.insert(new Node('\0', 0, null, null));
else pq.insert(new Node('\1', 0, null, null));
}
// merge two smallest trees
while (pq.size() > 1) {
Node left = pq.delMin();
Node right = pq.delMin();
Node parent = new Node('\0', left.freq + right.freq, left, right);
pq.insert(parent);
}
return pq.delMin();
}
// write bitstring-encoded trie to standard output
private static void writeTrie(Node x) {
if (x.isLeaf()) {
BinaryStdOut.write(true);
BinaryStdOut.write(x.ch, 8);
return;
}
BinaryStdOut.write(false);
writeTrie(x.left);
writeTrie(x.right);
}
// make a lookup table from symbols and their encodings
private static void buildCode(String[] st, Node x, String s) {
if (!x.isLeaf()) {
buildCode(st, x.left, s + '0');
buildCode(st, x.right, s + '1');
}
else {
st[x.ch] = s;
}
}
// expand Huffman-encoded input from standard input and write to standard output
public static void expand() {
// read in Huffman trie from input stream
Node root = readTrie();
// number of bytes to write
int length = BinaryStdIn.readInt();
// decode using the Huffman trie
for (int i = 0; i < length; i++) {
Node x = root;
while (!x.isLeaf()) {
boolean bit = BinaryStdIn.readBoolean();
if (bit) x = x.right;
else x = x.left;
}
BinaryStdOut.write(x.ch, 8);
}
BinaryStdOut.close();
}
private static Node readTrie() {
boolean isLeaf = BinaryStdIn.readBoolean();
if (isLeaf) {
return new Node(BinaryStdIn.readChar(), -1, null, null);
}
else {
return new Node('\0', -1, readTrie(), readTrie());
}
}
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 2002-2012, Robert Sedgewick and Kevin Wayne.
*
* This file is part of algs4-package.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-package.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-package.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-package.jar. If not, see http://www.gnu.org/licenses.
*************************************************************************/