You will construct a Huffman tree based on the given frequencies of 26 English alphabets in upper case plus the space character. An internal tree node class in HuffmanTree with necessary information is required.

You will not randomly switch left and right children when merger two trees. Instead, you will build a right-heavy tree according to the following strategies to select the right child.

(1) The tree that is taller will be the right child, i.e., the height is greater; (2) If the two tree of the same height, then the tree with more nodes will be the right child; (3) If (1) and (2) fail to discriminate, then the sum of the ASCII values of the alphabets in the tree is greater will be the right child. Use the same criteria if frequency is not sufficient to decide which two trees should be merged.

(1) HuffmanTree(char[] a, int[] f) This is a constructor that builds a Huffman tree based on a and f, where a is an array of characters to be encoded and f is an array of frequencies corresponding to the characters in a. For example, if a[3] = D and f[3] = 43, that means the frequency of D is 43.

(2) public void printCodeWords() This method prints out all codewords in the Huffman tree from left leaves to right leaves in the tree. Use the following format: Huffman Codes: E[69]:000 (127) H[72]:0010 (61) S[82]:0011 (63) ..... Z[90]:1111111111 (1) The 0-1 string indicates that 000 is the Huffman code for E, [69] indicates the ASCII value of character E, and (127) is the frequency; same to characters H, S and Z.

(3) public String encode(String text) This method will return a 0-1 String using the Huffman codes. For example, encode("EHS") should return "00000100011".

(4) public String decode(String codeString) The reverse of the function above. For example, decode("00000100011") returns "EHS". -------------------------------------------------------------------------------------------------------------------------- Here is the driver and huffman tree node provided

/** * You should not modify this program. You should develop your own * HuffmanTree.java and put it in the package, myUtil. * * @author cli2 * */ import myUtil.HuffmanTree;

public class Asg7 { // this example is extended from Corman's book static public void CormanFrequency() { int[] f = {82,15,29,43,127,22,20,61,70,5,8,40,24,67,75,19,4,60,63,91,28,10,23,2,21,1,123}; char[] a = {'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',' '}; HuffmanTree ht = new HuffmanTree(a, f); // Construct a Huffman Tree based on a and f ht.printCodeWords(); System.out.printf("%nCode: %s%n", ht.encodeToStr("HUFFMAN ENCODING IS VERY USEFUL")); System.out.printf("%nText: %s%n", ht.decodeFromStr("00100111011110011110011111011001000010000100001111101011010100110001101100101001001101010111110000110110111010011111010101010110")); System.out.printf("%nText: %s%n", ht.decodeFromStr("0111101101101111011101110101011011001101100101110001011011101010010011010111100011101000")); System.out.printf("%nText: %s%n", ht.decodeFromStr("11100010100100110101001001101011100010000010101101100001111100101100001100111001110110100011111000010001110")); } public static void main(String[] args) { CormanFrequency(); }

}

private class HTreeNode {

private int f;

private char a;

private HTreeNode left, right;

private HTreeNode(char a, int f) {

this.a = a;

Someone previously submitted the following code which does not work:

public class HuffmanTree {

private int size = 0; private HuffNode root = new HuffNode(); private PriorityQueue huffQueue = new PriorityQueue(); public ArrayList pathTable = new ArrayList(); public ArrayList valueTable = new ArrayList();

public HuffmanTree(char[] code, int[] freq) { // get the counts this.size = freq.length;

// throw exception if arrays are different sizes if (freq.length != code.length) { throw new UnsupportedOperationException("Error: Character and code length mismatch."); }

// build huffQueue from frequencies given for (int i = 0; i < this.size; i++) { huffQueue.offer(new HuffNode(code[i], freq[i], null, null, null)); }

// build huffman tree from queue createTree();

// build code table from huffman tree createTable(this.root, ""); }

/** * creates code table for a huffman tree * * @param HuffNode * -- root for tree, string -- for building paths */ private void createTable(HuffNode curr, String str) { // if iterator is null, return if (curr == null) return;

// else if leaf, display path and value if (curr.leftTree == null && curr.rightTree == null) { char tempChar; if (curr.value == 32) tempChar = ' ';

if (curr.value == 10) tempChar = 'n';

else tempChar = (char) curr.value; // add value and path to code tables this.valueTable.add(tempChar); this.pathTable.add(str); }

// add 0 if before moving to left child str += "0"; // recursively call in pre-order createTable(curr.leftTree, str);

// adjust path and add 1 before moving to right child str = str.substring(0, str.length() - 1); str += "1"; createTable(curr.rightTree, str); }

/** * creates Huffman Tree from frequencies and values * * @param null */ private void createTree() { // while elements remain in huffQueue, add to tree while (huffQueue.size() > 1) { // pop off two minimum elements in huffQueue HuffNode tempL = huffQueue.poll(); HuffNode tempR = huffQueue.poll();

// create root for two minimum elements and build tree HuffNode parent = new HuffNode(0, tempL.weight + tempR.weight, tempL, tempR, null); tempL.parent = parent; tempR.parent = parent;

// add new tree back in huffQueue huffQueue.offer(parent); this.size++; }

// set HuffTree root to remaining element in huffQueue this.root = huffQueue.peek(); }

public void printCodeWords() { System.out.println("Display Tree:"); HuffNode curr = this.root; this.getTree(curr); System.out.println("");

}

/** * returns decoded string for a given set of bits * * @param String * -- bits to be decoded * @return String -- decoded version of bits */ public String decodeFromStr(String bits) { // create empty string to hold decoded message String decodedStr = "";

// iterate through bits for (int i = 0; i < bits.length(); i++) { if (!getChar(bits.substring(0, i + 1)).equals("")) { decodedStr += getChar(bits.substring(0, i + 1)); bits = bits.substring(i + 1); i = 0; } } return decodedStr; }

/** * returns encoded bits for a given string * * @param String * -- to be encoded * @return String -- encoded version of original string */ public String encodeToStr(String input) { // create empty string to hold code String str = "";

// iterate through given string for (int x = 0; x < input.length(); x++) { // iterate through code tables for (int i = 0; i < valueTable.size(); i++) { // if char in string matches code in table, add path to string if (valueTable.get(i) == input.charAt(x)) str += pathTable.get(i); } } return str; }

/** * returns character for a given set of bits * * @param String * -- bits to be checked * @return String -- character associated with bits if any */ private String getChar(String bits) { // create string to hold potential character String character = ""; // traverse code table to seek match for (int i = 0; i < pathTable.size(); i++) { // add to string if match is found if (pathTable.get(i).equals(bits)) character = valueTable.get(i).toString(); } return character; }

/** * display given huffman tree using pre-order traversal * * @param HuffNode * -- root of tree to be displayed */ // global variable used for representing 'levels' of tree String tacks = "";

public void getTree(HuffNode curr) { // if iterator is null, return if (curr == null) return;

// else if leaf, display level, weight, and value if (curr.leftTree == null && curr.rightTree == null) { // case statements to handle displaying space and newline switch (curr.value) { case 32: System.out.println(tacks + curr.weight + ": sp"); break; case 10: System.out.println(tacks + curr.weight + ": nl"); break; default: System.out.println(tacks + curr.weight + ": " + (char) curr.value); break; } } }

private class HuffNode implements Comparable {

public int value; public int weight; public HuffNode leftTree; public HuffNode rightTree; public HuffNode parent;

// constructors public HuffNode() { parent = null; }

public HuffNode(int v, int w, HuffNode lTree, HuffNode rTree, HuffNode par) { value = v; weight = w; leftTree = lTree; rightTree = rTree; parent = par; }

@Override public int compareTo(HuffNode o) { // TODO Auto-generated method stub return 0; }

}

this.f = f; left = right = null;

}

private HTreeNode(HTreeNode left, HTreeNode right) {

a = (char)0;

f = left.f+right.f;

this.left = left;

this.right = right;

}

}

Output should be in following format

Huffman Codes:

E[69]:000 (127)

H[72]:0010 (61)

S[82]:0011 (63)