Huffman

代码说明：

  哈弗曼编码，构造哈夫曼树，构造哈夫曼树非常简单，将所有的节点放到一个队列中，用一个节点替换两个频率最低的节点，新节点的频率就是这两个节点的频率之和。这样，新节点就是两个被替换节点的父节点了。如此循环，直到队列中只剩一个节点（树根）。(Hoffman coding, Huffman tree structure, Huffman tree structure is very simple, all the nodes in a queue, replace the two lowest frequency node with a node, the new node and the frequency of frequency is the two nodes. So, the new node is two replaced node parent node. So the cycle, until the queue is only one node (Shu Gen). )