Huffman coding

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

struct MinHeapNode{
    char data;
    unsigned freq;
    MinHeapNode *left, *right;

    MinHeapNode(char data, unsigned freq)
    {
        left = right = NULL;
        this->data = data;
        this->freq = freq;
    }
};

struct compare{

    bool operator()(MinHeapNode* l, MinHeapNode* r)
    {
        return (l->freq > r->freq);
    }
};

void printCodes(struct MinHeapNode* root, string str)
{
    if(!root)
        return;

    if(root->data != '$')
        cout<<root->data<<": "<<str<<"\n";

    printCodes(root->left, str+"0");
    printCodes(root->right, str+"1");
}

void HuffmanCode(char data[], int freq[], int size)
{
    struct MinHeapNode *left, *right, *top;

    priority_queue<MinHeapNode*, vector<MinHeapNode*>, compare>minHeap;

    for(int i = 0; i<size; ++i)
    {
        minHeap.push(new MinHeapNode(data[i],freq[i]));
    }

    while(minHeap.size() != 1){
        left = minHeap.top();
        minHeap.pop();

        right = minHeap.top();
        minHeap.pop();

        top = new MinHeapNode('$',left->freq+right->freq);

        top->left = left;
        top->right = right;

        minHeap.push(top);
    }
    printCodes(minHeap.top(),"");
}

int main()
{
    char arr[] = {'a','b','c','d','e','f'};
    int freq[] = {5,9,12,13,16,45};

    int size = sizeof(arr)/sizeof(arr[0]);

    HuffmanCode(arr, freq, size);

    return 0;


}