Leetcode Validate Binary Search Tree

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.

注意本题在原有的函数上添加了默认参数，以便形成递归

class Solution {
public:
bool isValidBST(TreeNode *root,int min = INT_MIN,int max = INT_MAX){
if(!root) return true;
if(root->val <= min || root->val>=max) return false;
return isValidBST(root->left,min,root->val) && isValidBST(root->right,root->val, max);
}
};