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.
/** * 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 isValidBST(TreeNode *root) { // Start typing your C/C++ solution below // DO NOT write int main() function int pre=INT_MIN; return inorder(root,pre); } bool inorder(TreeNode* root,int& pre) { if (!root ) return true; if (!inorder(root->left,pre)) return false; if ( pre>=root->val) return false; pre=root->val; return inorder(root->right,pre); } };