本程序可以用三种方法建立二叉树，并实现相应功能。1、通过输入树的嵌套括号表示序列建立二叉树；2、根据前序遍历序列和中序遍历序列建立二叉树；3、建立哈夫曼树-This program can use three ways to establish a binary tree, and to achieve that function. 1, by entering the tree to establish a sequence of nested parentheses binary tree　2, according to preorder traversal sequences and the establishment of a binary tree in order traversal sequences　3, the establishment of Huffman tree