Homework 3 Huffman Coding. Due Thursday October 11

Transcription

1 Homework 3 Huffman Coding Due Thursday October 11

2 Huffman Coding Implement Huffman Encoding and Decoding and the classes shown on the following slides. You will also need to use Java s stack class HuffmanEncode expects 2 command line arguments: the name of the source file (the file to be compressed) and the name of the destination file (the file to which the compressed file must be written)

3 Huffman Coding HuffmanDecode expects 2 command line arguments: the name of the source file (a file that contains a compressed file created by your encoder) and the name of the destination file (the file to which the uncompressed file must be written) If your programs work the contents of decoder s destination file should be exactly the same as the original source file used by encoder

4 Huffman Coding I will post some large files for you to test with but you should first test with small files you create The source file to encode will only include characters with character codes between 0 and 127 inclusive You will demonstrate your implementation to me (see submission slides).

5 HuffmanOutputStream import java.io.*; public class HuffmanOutputStream { //add additional private variables as needed //do not modify the public methods signatures or add public methods DataOutputStream d; public HuffmanOutputStream(String filename, String tree, int totalchars) { try { d = new DataOutputStream(new FileOutputStream(filename)); d.writeutf(tree); d.writeint(totalchars); catch (IOException e) { //add other initialization statements as needed

6 HuffmanOutputStream public void writebit(char bit) { //PRE:bit == '0' bit == '1' public void close() { //write final byte (if needed) //close the DataOutputStream

7 Huffman Input Stream import java.io.*; public class HuffmanInputStream { //add additional private variables and methods as needed //DO NOT modify the public method signatures or add public methods private String tree; private int totalchars; private DataInputStream d; public HuffmanInputStream(String filename) { try { d = new DataInputStream(new FileInputStream(filename)); tree = d.readutf(); totalchars = d.readint(); catch (IOException e) { //add other initialization statements as needed

8 Huffman Input Stream public int readbit() { //returns the next bit is the file //the value returned will be either a 0 or a 1 public String gettree() { //return the tree representation read from the file public int gettotalchars() { //return the character count read from the file

9 Huffman Tree import java.util.*; public class HuffmanTree { //DO NOT include the frequency or priority in the tree private class Node { private Node left; private char data; private Node right; private Node parent; private Node(Node L, char d, Node R, Node P) { left = L; data = d; right = R; parent = P; private Node root; private Node current; //this value is changed by the move methods

10 Huffman Tree public HuffmanTree() { root = null; current = null; public HuffmanTree(char d) { //makes a single node tree public HuffmanTree(String t, char nonleaf) { //Assumes t represents a post order representation of the tree as discussed // in class //nonleaf is the char value of the data in the non-leaf nodes //in classs we used (char) 128 for the non-leaf value public HuffmanTree(HuffmanTree b1, HuffmanTree b2, char d) { //makes a new tree where b1 is the left subtree and b2 is the right subtree //d is the data in the root

11 Huffman Tree //use the move methods to traverse the tree //the move methods change the value of current //use these in the decoding process public void movetoroot() { //change current to reference the root of the tree public void movetoleft() { //PRE: the current node is not a leaf //change current to reference the left child of the current node public void movetoright() { //PRE: the current node is not a leaf //change current to reference the right child of the current node public void movetoparent() { //PRE: the current node is not the root //change current to reference the parent of the current node

12 Huffman Tree public boolean atroot() { //returns true if the current node is the root otherwise returns false public boolean atleaf() { //returns true if current references a leaf other wise returns false public char current() { //returns the data value in the node referenced by current

13 Huffman Tree public class PathIterator implements Iterator<String> { //the iterator returns the path (a series of 0s and 1s) to each leaf //DO NOT compute all paths in the constructor //only compute them as needed (similar to what you did in homework 2) //add private methods and variables as needed public PathIterator() { public boolean hasnext() { public String next() { //the format of the string should be leaf value, a space, a sequence of //0s and 1s //the 0s and 1s indicate the path from the root the node containing //the leaf value public void remove() { //optional method not implemented

14 Huffman Tree public Iterator<String> iterator() { //return a new path iterator object public String tostring() { //returns a string representation of the tree using the postorder format // discussed in class

15 Binary Heap public class BinaryHeap { //implements a binary heap where the heap rule is the value in the parent //node is less than //or equal to the values in the child nodes //the implementation uses parallel arrays to store the priorities and the // trees //you must use this implementation int priority[]; HuffmanTree trees[]; int size; public BinaryHeap(int s) { priority = new int[s+1]; trees = new HuffmanTree[s+1]; size = 0;

16 Binary Heap public void removemin() { //PRE: size!= 0 //removes the priority and tree at the root of the heap public int getminpriority() { //PRE: size!= 0 //return the priority in the root of the heap public HuffmanTree getmintree() { //PRE: size!= 0 //return the tree in the root of the heap

17 Binary Heap public boolean full() { //return true if the heap is full otherwise return false public void insert(int p, HuffmanTree t) { //insert the priority p and the associated tree t into the heap //PRE!full() public int getsize() { //return the number of values (priority, tree) pairs in the heap

18 Huffman Encode import java.io.*; import java.util.*; public class HuffmanEncode { public HuffmanEncode(String in, String out) { //Implements the Huffman encoding algorithm //Add private methods and instance variables as needed public static void main(string args[]) { //args[0] is the name of the file whose contents should be compressed //args[1] is the name of the output file that will hold the compressed //content of the input file new HuffmanEncode(args[0], args[1]); //do not add anything here

19 Huffman Decode import java.io.*; import java.util.*; public class HuffmanDecode { public HuffmanDecode(String in, String out) { //implements the Huffman Decode Algorithm //Add private methods and instance variables as needed public static void main(string args[]) { //args[0] is the name of a input file (a file created by Huffman Encode) //args[1] is the name of the output file for the uncompressed file new HuffmanDecode(args[0], args[1]); //do not add anything here

20 Homework 3 There are multiple ways you could organize a solution to Huffman coding. For example instead of implementing your our priority queue you could use Java's priority queue or you could include the priority of a Huffman tree with the Huffman tree object. For this homework you MUST implement the solution using the organization I gave you.

21 Homework 3 Submission You will demonstrate your program to me either on your own machine or on a machine in the CS lab me your source code (as multiple java files attached to the ) after you demo.

22 Homework 3 Demonstration The demonstration will consist of 2 parts. In the first part you will compress and uncompress some files. In the terminal window (Mac or Linux) or the command prompt (Windows) we will look at the size of the files and check that the decoded files match the original files. To check that the decoded files match the originals we will use diff in the terminal window (Mac or Linux) or fc in the command prompt (Windows). You will need to navigate to your files in the terminal window or command prompt. For the second part of the demonstration I will ask you questions about your code.