huffmandecoding.cpp

// C++ program to encode and decode a string using 
// Huffman Coding. 
#include <bits/stdc++.h> 
#define MAX_TREE_HT 256 
using namespace std; 

// to map each character its huffman value 
map<char, string> codes; 

// to store the frequency of character of the input data 
map<char, int> freq; 

// A Huffman tree node 
struct MinHeapNode 
{ 
	char data;			 // One of the input characters 
	int freq;			 // Frequency of the character 
	MinHeapNode *left, *right; // Left and right child 

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

// utility function for the priority queue 
struct compare 
{ 
	bool operator()(MinHeapNode* l, MinHeapNode* r) 
	{ 
		return (l->freq > r->freq); 
	} 
}; 

// utility function to print characters along with 
// there huffman value 
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"); 
} 

// utility function to store characters along with 
// there huffman value in a hash table, here we 
// have C++ STL map 
void storeCodes(struct MinHeapNode* root, string str) 
{ 
	if (root==NULL) 
		return; 
	if (root->data != '$') 
		codes[root->data]=str; 
	storeCodes(root->left, str + "0"); 
	storeCodes(root->right, str + "1"); 
} 

// STL priority queue to store heap tree, with respect 
// to their heap root node value 
priority_queue<MinHeapNode*, vector<MinHeapNode*>, compare> minHeap; 

// function to build the Huffman tree and store it 
// in minHeap 
void HuffmanCodes(int size) 
{ 
	struct MinHeapNode *left, *right, *top; 
	for (map<char, int>::iterator v=freq.begin(); v!=freq.end(); v++) 
		minHeap.push(new MinHeapNode(v->first, v->second)); 
	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); 
	} 
	storeCodes(minHeap.top(), ""); 
} 

// utility function to store map each character with its 
// frequency in input string 
void calcFreq(string str, int n) 
{ 
	for (int i=0; i<str.size(); i++) 
		freq[str[i]]++; 
} 

// function iterates through the encoded string s 
// if s[i]=='1' then move to node->right 
// if s[i]=='0' then move to node->left 
// if leaf node append the node->data to our output string 
string decode_file(struct MinHeapNode* root, string s) 
{ 
	string ans = ""; 
	struct MinHeapNode* curr = root; 
	for (int i=0;i<s.size();i++) 
	{ 
		if (s[i] == '0') 
		curr = curr->left; 
		else
		curr = curr->right; 

		// reached leaf node 
		if (curr->left==NULL and curr->right==NULL) 
		{ 
			ans += curr->data; 
			curr = root; 
		} 
	} 
	// cout<<ans<<endl; 
	return ans+'\0'; 
} 

// Driver program to test above functions 
int main() 
{ 
	string str = "geeksforgeeks"; 
	string encodedString, decodedString; 
	calcFreq(str, str.length()); 
	HuffmanCodes(str.length()); 
	cout << "Character With there Frequencies:\n"; 
	for (auto v=codes.begin(); v!=codes.end(); v++) 
		cout << v->first <<' ' << v->second << endl; 

	for (auto i: str) 
		encodedString+=codes[i]; 

	cout << "\nEncoded Huffman data:\n" << encodedString << endl; 

	decodedString = decode_file(minHeap.top(), encodedString); 
	cout << "\nDecoded Huffman Data:\n" << decodedString << endl; 
	return 0; 
}