生成二叉树

按照普通的二叉树输入方法进行输入，空节点还是用@表示。

例如输入以下这棵树：

A

/ B C

/ D E

/ F G

输入根节点:A

输入A的两个儿子(@表示空节点):BC

输入B的两个儿子(@表示空节点):@@

输入C的两个儿子(@表示空节点):DE

输入D的两个儿子(@表示空节点):FG

输入E的两个儿子(@表示空节点):@@

输入F的两个儿子(@表示空节点):@@

输入G的两个儿子(@表示空节点):-Generate binary input method in accordance with the ordinary binary input, represented by an empty node or @. For example, enter the following tree: A/\ BC/\ DE/\ FG enter the root node: A Enter the two sons of A (@ represents an empty node): BC enter two sons of B (@ represents an empty node): @ Enter the two sons of C @ (@ represents an empty node): two sons DE input of D (@ represents an empty node): two sons FG input E (@ represents an empty node): Enter the two sons of F@@ (@ represents the empty node): Enter the two sons of G@@(@ represents an empty node):@@