这是树的应用——哈夫曼编码，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-This is the application of tree- Huffman coding, a number of characters from the keyboard input and the frequency of each character, the character frequency as node weights set u