说明：  利用哈夫曼编码进行通信可以大大提高信道的利用率，缩短信息传输的时间，降低传输成本。根据哈夫曼编码的原理，编写一个程序，在用户输入结点权值的基础上求哈夫曼编码。 要求：从键盘输入若干字符及每个字符出现的频率，将字符出现的频率作为结点的权值，建立哈夫曼树，然后对各个字符进行哈夫曼编码，最后打印输出字符及对应的哈夫曼编码。
(Communicate using Huffman coding can greatly improve the utilization of the channel, reducing the time information transmission and reduce transmission costs. According to Huffman coding theory, write a program, the user input node based on the weight of demand Huffman coding. Requirements: Some characters from the keyboard and the frequency of each character, the character frequency of occurrence as the weight of node, the establishment of Huffman tree, and then Huffman coding the various characters, and finally print out characters and the corresponding Huffman coding.)