PAT A1099 Build A Binary Search Tree (30 分)——二叉搜索树,中序遍历,层序遍历
ABinarySearchTree(BST)isrecursivelydefinedasabinarytreewhichhasthefollowingproperties:Theleftsubtreeofanodecontainsonlynodeswithkeyslessthanthenode'skey.Therightsubtreeofanodecontainsonlynodeswithkeys