从文件中读入字符集大小n，以及n个字符和n个权值。构建哈夫曼树，对每个字符生成哈夫曼编码。从文件中读入需编码的字符串，利用哈夫曼编码，对字符串进行编码，编码结果保存在文件。-The character read from the file set size n, and n-n character and the right values. Construction of Huffman tree generated Huffman code for each character. Read f