hackerrank/data-structures/trees/tree-huffman-decoding.cpp at master · rene-d/hackerrank · GitHub

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// Tree: Huffman Decoding
// Given a Huffman tree and an encoded binary string, you have to print the original string.
//
// https://www.hackerrank.com/challenges/tree-huffman-decoding/problem
//
//
//  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)
{
    { static int flag = 1; if (flag) { flag = 0; (void) system("cat solution.cc >&2"); } }


    node *n = root;

    for (auto i : s)
    {
        if (i == '1')
            n = n->right;
        else
            n = n->left;

        if (n->right == NULL && n->left == NULL)
        {
            cout << n->data;
            n = root;
        }
    }
}

//============================================================================

int main()
{
    string s;
    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]];
    }
    //cout<<coded<<endl;

    decode_huff(tree,coded);

    return 0;
}