从键盘输入若干字符，统计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，最后打印输出每个字符及对应的哈夫曼编-Enter the number of characters from the keyboard, statistics, the frequency of each character, the character frequency of occurrence as the node weights to build the Huffman tree, and then Huffman coding of individual characters, and finally print out each character and the corresponding Huffman Code