In this HackerRank Tree: Huffman Decoding Interview preparation kit problem You are given a pointer to the root of the Huffman tree and a binary coded string to decode. You need to print the decoded string.

HackerRank Tree: Huffman Decoding Interview preparation kit solution


Problem solution in Python programming.

import queue as Queue

cntr = 0

class Node:
    def __init__(self, freq, data):
        self.freq = freq
        self.data = data
        self.left = None
        self.right = None
        global cntr
        self._count = cntr
        cntr = cntr + 1
        
    def __lt__(self, other):
        if self.freq != other.freq:
            return self.freq < other.freq
        return self._count < other._count

def huffman_hidden():#builds the tree and returns root
    q = Queue.PriorityQueue()

    
    for key in freq:
        q.put((freq[key], key, Node(freq[key], key) ))
    
    while q.qsize() != 1:
        a = q.get()
        b = q.get()
        obj = Node(a[0] + b[0], '\0' )
        obj.left = a[2]
        obj.right = b[2]
        q.put((obj.freq, obj.data, obj ))
        
    root = q.get()
    root = root[2]#contains root object
    return root

def dfs_hidden(obj, already):
    if(obj == None):
        return
    elif(obj.data != '\0'):
        code_hidden[obj.data] = already
        
    dfs_hidden(obj.right, already + "1")
    dfs_hidden(obj.left, already + "0")

"""class Node:
    def __init__(self, freq,data):
        self.freq= freq
        self.data=data
        self.left = None
        self.right = None
"""        

# Enter your code here. Read input from STDIN. Print output to STDOUT
def decodeHuff(root, s):
    #Enter Your Code Here
    cur = root
    chararray = []
    #For each character, 
    #If at an internal node, move left if 0, right if 1
    #If at a leaf (no children), record data and jump back to root AFTER processing character
    for c in s:
        if c == '0' and cur.left:
            cur = cur.left
        elif cur.right:
            cur = cur.right
        
        if cur.left is None and cur.right is None:
            chararray.append(cur.data)
            cur = root
    
    #Print final array
    print("".join(chararray))

ip = input()
freq = {}#maps each character to its frequency

cntr = 0

for ch in ip:
    if(freq.get(ch) == None):
        freq[ch] = 1
    else:
        freq[ch]+=1

root = huffman_hidden()#contains root of huffman tree

code_hidden = {}#contains code for each object

dfs_hidden(root, "")

if len(code_hidden) == 1:#if there is only one character in the i/p
    for key in code_hidden:
        code_hidden[key] = "0"

toBeDecoded = ""

for ch in ip:
   toBeDecoded += code_hidden[ch]

decodeHuff(root, toBeDecoded)




Problem solution in Java Programming.

import java.util.*;
 
abstract class Node implements Comparable<Node> {
    public  int frequency; // the frequency of this tree
    public  char data;
    public  Node left, right; 
    public Node(int freq) { 
      frequency = freq; 
    }
 
    // compares on the frequency
    public int compareTo(Node tree) {
        return frequency - tree.frequency;
    }
}
 
class HuffmanLeaf extends Node {
    
 
    public HuffmanLeaf(int freq, char val) {
        super(freq);
        data = val;
    }
}
 
class HuffmanNode extends Node {
    
    public HuffmanNode(Node l, Node r) {
        super(l.frequency + r.frequency);
        left = l;
        right = r;
    }

}


class Decoding {

/*  
  class Node
    public  int frequency; // the frequency of this tree
      public  char data;
      public  Node left, right;
    
*/ 

  void decode(String S, Node root)
{
    StringBuilder sb = new StringBuilder();
    Node c = root;
    for (int i = 0; i < S.length(); i++) {
        c = S.charAt(i) == '1' ? c.right : c.left;
        if (c.left == null && c.right == null) {
            sb.append(c.data);
            c = root;
        }
    }
    System.out.print(sb);
}



}

 
public class Solution {
  
    // input is an array of frequencies, indexed by character code
    public static Node buildTree(int[] charFreqs) {
      
        PriorityQueue<Node> trees = new PriorityQueue<Node>();
        // initially, we have a forest of leaves
        // one for each non-empty character
        for (int i = 0; i < charFreqs.length; i++)
            if (charFreqs[i] > 0)
                trees.offer(new HuffmanLeaf(charFreqs[i], (char)i));
 
        assert trees.size() > 0;
      
        // loop until there is only one tree left
        while (trees.size() > 1) {
            // two trees with least frequency
            Node a = trees.poll();
            Node b = trees.poll();
 
            // put into new node and re-insert into queue
            trees.offer(new HuffmanNode(a, b));
        }
      
        return trees.poll();
    }
  
    public static Map<Character,String> mapA=new HashMap<Character ,String>();
  
    public static void printCodes(Node tree, StringBuffer prefix) {
      
        assert tree != null;
      
        if (tree instanceof HuffmanLeaf) {
            HuffmanLeaf leaf = (HuffmanLeaf)tree;
 
            // print out character, frequency, and code for this leaf (which is just the prefix)
            //System.out.println(leaf.data + "\t" + leaf.frequency + "\t" + prefix);
            mapA.put(leaf.data,prefix.toString());

        } else if (tree instanceof HuffmanNode) {
            HuffmanNode node = (HuffmanNode)tree;
 
            // traverse left
            prefix.append('0');
            printCodes(node.left, prefix);
            prefix.deleteCharAt(prefix.length()-1);
 
            // traverse right
            prefix.append('1');
            printCodes(node.right, prefix);
            prefix.deleteCharAt(prefix.length()-1);
        }
    }
 
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
    
        String test= input.next();
 
        // we will assume that all our characters will have
        // code less than 256, for simplicity
        int[] charFreqs = new int[256];
      
        // read each character and record the frequencies
        for (char c : test.toCharArray())
            charFreqs[c]++;
 
        // build tree
        Node tree = buildTree(charFreqs);
 
        // print out results
        printCodes(tree, new StringBuffer());
        StringBuffer s = new StringBuffer();
      
        for(int i = 0; i < test.length(); i++) {
            char c = test.charAt(i);
            s.append(mapA.get(c));
        }
      
        //System.out.println(s);
        Decoding d = new Decoding();
        d.decode(s.toString(), tree);

    }
}


Problem solution in C++ programming.

//
//  main.cpp
//  Huffman
//
//  Created by Vatsal Chanana

#include<bits/stdc++.h>
using namespace std;

typedef struct node {
    int freq;
    char data;
    node * left;
    node * right;
} node;

struct deref:public binary_function<node*, node*, bool> {
    bool operator()(const node * a, const node * b)const {
        return a->freq > b->freq;
    }
};

typedef priority_queue<node *, vector<node*>, deref> spq;

node * huffman_hidden(string s) {

    spq pq;
    vector<int>count(256,0);
  
    for(int i = 0; i < s.length(); i++ ) {
        count[s[i]]++;
    }
    
    for(int i=0; i < 256; i++) {
        
        node * n_node = new node;
        n_node->left = NULL;
        n_node->right = NULL;
        n_node->data = (char)i;
        n_node->freq = count[i];
      
        if( count[i] != 0 )
            pq.push(n_node);
      
    }
    
    while( pq.size() != 1 ) {
      
        node * left = pq.top();
        pq.pop();
        node * right = pq.top();
        pq.pop();
        node * comb = new node;
        comb->freq = left->freq + right->freq;
        comb->data = '\0';
        comb->left = left;
        comb->right = right;
        pq.push(comb);
      
    }
    
    return pq.top();
    
}

void print_codes_hidden(node * root, string code, map<char, string>&mp) {
    
    if(root == NULL)
        return;
    
    if(root->data != '\0') {
        mp[root->data] = code;
    }
  
    print_codes_hidden(root->left, code+'0', mp);
    print_codes_hidden(root->right, code+'1', mp);
        
}

/* 
The structure of the node is

typedef struct node {

    int freq;
    char data;
    node * left;
    node * right;
    
} node;

*/


void decode_huff(node * root,string s)
{
    string ans = "";
    node* n = root;
    for(auto itr = s.begin(); itr != s.end();itr++){
        node* next;
        if(*itr == '0'){
            next = n -> left;
        }
        else{
            next = n -> right;
        }
        if(next -> data == '\0'){
            n = next;
        }
        else{
            ans += next -> data;
            n = root;
        }
    }
    cout << ans << endl;
}

int main() {
  
    string s;
    std::cin >> s;
  
    node * tree = huffman_hidden(s);
    string code = "";
    map<char, string>mp;
  
    print_codes_hidden(tree, code, mp);
    
    string coded;
  
    for( int i = 0; i < s.length(); i++ ) {
        coded += mp[s[i]];
    }
    
    decode_huff(tree,coded);
  
    return 0;
}