Given a binary tree, determine if it is a valid binary search tree (BST).
Assume a BST is defined as follows:
The left subtree of a node contains only nodes with keys less than the node's...
[leetcode] 98. validate binary search tree 验证二叉搜索树
given a binary tree, determine if it is a valid binary search tree (bst).
assume a bst is defined as follows:
the left subtree of a node c...