[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.
OJ's Binary Tree Serialization:
The serialization of a binary tree follows a level order traversal, where '#' signifies a path terminator where no node exists below.
Here's an example:
1
/ \
2 3
/
4
\
5
The above binary tree is serialized as
"{1,2,3,#,#,4,#,#,5}".
思考：记录parent有点繁，记录上下界。
/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
bool DFS(TreeNode *root,int min,int max)
{
if(root)
{
if(min<root->val&&root->val<max)
{
return DFS(root->left,min,root->val)&&DFS(root->right,root->val,max);
}
else return false;
}
else return true;
}
bool isValidBST(TreeNode *root) {
return DFS(root,INT_MIN,INT_MAX);
}
};