Huffman Coding implemented.. asked by amazon often times

Author: kaidul

.DS_Store

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+.DS_Store

.gitignore

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 + [N-Queen](algorithms/nqueen.cpp)
 + [Prime Ring](algorithms/prime_ring.cpp)
 
+### Greedy Algorithm
++ [Huffman Coding](algorithms/Huffman_coding.cpp)
+
 ### String Algorithm
 + [Aho-Corasick Algorithm](algorithms/Aho_Corasick.cpp)
 + [Knuth-Morris-Pratt’s Algorithm](algorithms/kmp.cpp)

README.md

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+// A Huffman tree node
+struct MinHeapNode {
+    char data;                 // One of the input characters
+    unsigned freq;             // Frequency of the character
+    MinHeapNode *left, *right; // Left and right child
+    MinHeapNode(char data, unsigned freq): data(data), freq(freq), left(nullptr), right(nullptr) {
+    }
+};
+
+struct compare {
+    bool operator()(MinHeapNode* lhs, MinHeapNode* rhs) {
+        return (lhs->freq > rhs->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 huffmanCodes(unordered_map<char, int>& freqMap) {
+    priority_queue<MinHeapNode*, vector<MinHeapNode*>, compare> minHeap;
+    for(auto iter = freqMap.begin(); iter != freqMap.end(); ++iter) {
+        minHeap.push(new MinHeapNode(iter->first, iter->second));
+    }
+    while (minHeap.size() != 1) {
+        MinHeapNode* left = minHeap.top();
+        minHeap.pop();
+        MinHeapNode* right = minHeap.top();
+        minHeap.pop();
+        MinHeapNode* newNode = new MinHeapNode('#', left->freq + right->freq);
+        newNode->left = left;
+        newNode->right = right;
+        minHeap.push(newNode);
+    }
+    
+    printCodes(minHeap.top(), "");
+}