algorithm-examples/cpp-algorithm/src/greedy/huffman_code.h at main · codejsha/algorithm-examples · GitHub

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#ifndef CPP_ALGORITHM_HUFFMAN_CODE_H

#define CPP_ALGORITHM_HUFFMAN_CODE_H

#include <map>

#include <queue>

#include <string>

namespace Huffman

{

/**

* \brief Node in full binary tree for Huffman code.

struct HuffmanNode

{

HuffmanNode* left;

HuffmanNode* right;

int key;

char ch;

int freq;

HuffmanNode(const int key, const char ch, const int freq)

: left(nullptr), right(nullptr), key(key), ch(ch), freq(freq)

{

}

};

/**

* \brief Comparator for minimal heap builds

class MinComparator

{

public:

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

};

/**

* \brief Huffman code algorithm.

* \param freq_map a map of char and frequency pairs

* \return root node

HuffmanNode* HuffmanCode(const std::map<int, char>& freq_map);

/**

* \brief Tree traversal to get the Huffman code

* \param root root node that starts the tree traversal

* \param code prefix code

* \param result result of tree traversal

void TraversalHuffmanCode(

const HuffmanNode* root,

const std::string& code,

std::map<char, std::string>& result);

}

// ----------------------------------------------------------------------------

inline Huffman::HuffmanNode* Huffman::HuffmanCode(const std::map<int, char>& freq_map)

{

std::priority_queue<HuffmanNode*, std::vector<HuffmanNode*>, MinComparator> min_queue;

for (auto [freq, ch] : freq_map)

{

min_queue.push(new HuffmanNode{freq, ch, freq});

}

while (static_cast<int>(min_queue.size()) != 1)

{

const auto left = min_queue.top();

min_queue.pop();

const auto right = min_queue.top();

min_queue.pop();

const int key = left->key + right->key;

auto node = new HuffmanNode{key, '-', left->freq + right->freq};

node->left = left;

node->right = right;

min_queue.push(node);

}

return min_queue.top();

}

// ----------------------------------------------------------------------------

inline void Huffman::TraversalHuffmanCode(

const HuffmanNode* root,

const std::string& code,

std::map<char, std::string>& result)

{

if (root == nullptr)

{

return;

}

if (root->ch != '-')

{

result.insert(std::pair(root->ch, code));

}

TraversalHuffmanCode(root->left, code + "0", result);

TraversalHuffmanCode(root->right, code + "1", result);

}

#endif

algorithm-examples/cpp-algorithm/src/greedy/huffman_code.h at main · codejsha/algorithm-examples · GitHub

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