A binary search tree (BST) is a node based binary tree data structure which has the following properties.
- The left subtree of a node contains only nodes with keys
less than the node’s key. - The right subtree of a node contains only nodes with keys
greater than the node’s key. - Both the left and right subtrees must also be binary search
trees.
对二叉树进行中序遍历，判断该序列是否为升序序列