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Avast fork of https://github.com/nayuki/Huffman-Coding , it adds bytecompressor layer compatibility.
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/**
 *
 *  Copyright © 2013 Nayuki Minase
 *
 *  Permission is hereby granted, free of charge, to any person obtaining a copy of
 *  this software and associated documentation files (the "Software"), to deal in
 *  the Software without restriction, including without limitation the rights to
 *  use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
 *  the Software, and to permit persons to whom the Software is furnished to do so,
 *  subject to the following conditions:
 *
 *  * The above copyright notice and this permission notice shall be included in
 *    all copies or substantial portions of the Software.
 *
 *  * The Software is provided "as is", without warranty of any kind, express or
 *    implied, including but not limited to the warranties of merchantability,
 *    fitness for a particular purpose and noninfringement. In no event shall the
 *    authors or copyright holders be liable for any claim, damages or other
 *    liability, whether in an action of contract, tort or otherwise, arising from,
 *    out of or in connection with the Software or the use or other dealings in the
 *    Software.
 */

package nayuki.huffmancoding;

import java.util.ArrayList;
import java.util.List;


/**
 * A binary tree where each leaf codes a symbol, for representing Huffman codes. Immutable.
 */
/*
 * There are two main uses of a CodeTree:
 * - Read the 'root' field and walk through the tree to extract the desired information.
 * - Call getCode() to get the code for a symbol, provided that the symbol has a code.
 * 
 * The path to a leaf node determines the leaf's symbol's code. Starting from the root, going to the left child represents a 0, and going to the right child represents a 1.
 * Constraints:
 * - The tree must be complete, i.e. every leaf must have a symbol.
 * - No symbol occurs in two leaves.
 * - But not every symbol needs to be in the tree.
 * - The root must not be a leaf node.
 * Example:
 *   Huffman codes:
 *     0: Symbol A
 *     10: Symbol B
 *     110: Symbol C
 *     111: Symbol D
 *   Code tree:
 *       .
 *      / \
 *     A   .
 *        / \
 *       B   .
 *          / \
 *         C   D
 */
public final class CodeTree {
	
	public final InternalNode root;  // Not null
	
	// Stores the code for each symbol, or null if the symbol has no code.
	// For example, if symbol 5 has code 10011, then codes.get(5) is the list [1, 0, 0, 1, 1].
	private List> codes;
	
	
	
	// Every symbol in the tree 'root' must be strictly less than 'symbolLimit'.
	public CodeTree(InternalNode root, int symbolLimit) {
		if (root == null)
			throw new NullPointerException("Argument is null");
		this.root = root;
		
		codes = new ArrayList>();  // Initially all null
		for (int i = 0; i < symbolLimit; i++)
			codes.add(null);
		buildCodeList(root, new ArrayList());  // Fills 'codes' with appropriate data
	}
	
	
	private void buildCodeList(Node node, List prefix) {
		if (node instanceof InternalNode) {
			InternalNode internalNode = (InternalNode)node;
			
			prefix.add(0);
			buildCodeList(internalNode.leftChild , prefix);
			prefix.remove(prefix.size() - 1);
			
			prefix.add(1);
			buildCodeList(internalNode.rightChild, prefix);
			prefix.remove(prefix.size() - 1);
			
		} else if (node instanceof Leaf) {
			Leaf leaf = (Leaf)node;
			if (leaf.symbol >= codes.size())
				throw new IllegalArgumentException("Symbol exceeds symbol limit");
			if (codes.get(leaf.symbol) != null)
				throw new IllegalArgumentException("Symbol has more than one code");
			codes.set(leaf.symbol, new ArrayList(prefix));
			
		} else {
			throw new AssertionError("Illegal node type");
		}
	}
	
	
	
	public List getCode(int symbol) {
		if (symbol < 0)
			throw new IllegalArgumentException("Illegal symbol");
		else if (codes.get(symbol) == null)
			throw new IllegalArgumentException("No code for given symbol");
		else
			return codes.get(symbol);
	}
	
	
	// Returns a string showing all the codes in this tree. The format is subject to change. Useful for debugging.
	public String toString() {
		StringBuilder sb = new StringBuilder();
		toString("", root, sb);
		return sb.toString();
	}
	
	
	private static void toString(String prefix, Node node, StringBuilder sb) {
		if (node instanceof InternalNode) {
			InternalNode internalNode = (InternalNode)node;
			toString(prefix + "0", internalNode.leftChild , sb);
			toString(prefix + "1", internalNode.rightChild, sb);
		} else if (node instanceof Leaf) {
			sb.append(String.format("Code %s: Symbol %d%n", prefix, ((Leaf)node).symbol));
		} else {
			throw new AssertionError("Illegal node type");
		}
	}
	
}