Valid Binary Tree@leetcode

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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 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.

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

» Solve this problem

这个题思路比较简单，就是看左右子树是否符合BST的条件。但是，有一点需要注意的就是，左子树的所有结点都要比root小，右子树的所有结点都要比root大。这样就给了比较的时候一个range，范围，我们在递归的时候要把这个范围给传递进去。