输入字符序列，建立二叉链表。

（2）先序、中序、后序遍历二叉树:递归算法。

（3）先序遍历二叉树:非递归算法（最好也能实现中序，后序非递归算法）。

（4）求二叉树的叶子个数。

（5）借助队列实现二叉树的层次遍历。

　　　（6）在主函数中设计一个简单的菜单，分别调试上述算法。-Enter the character sequence to build the binary tree. (2) first order, in sequence, after the binary tree traversal: a recursive algorithm. (3) The first tree traversal: non-recursive algorithm (the best can achieve in sequence, after the non-recursive algorithm). (4) Find the number of leaves of the binary tree. (5) the level of aid queue binary tree traversal. (6) Design a simple menu in the main function, namely to debug these algorithms.