DAY0022.cpp

// 98. Validate Binary Search Tree
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
    public:
        bool isValidBST(TreeNode* root) {
            return root!=NULL&&validate(root,LONG_MAX,LONG_MIN);
        }
        bool validate(TreeNode*root,long max,long min){
            if(root==NULL) return true;
            if(root->val<=min||root->val>=max) return false;
            return validate(root->left,root->val,min)&&validate(root->right,max,root->val);
        }
    };