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28 | /**
* 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 check(TreeNode* node, long long int maxVal, long long int minVal) {
if (node == nullptr)
return true;
if (node->val >= maxVal || node->val <= minVal)
return false;
return check(node->left, node->val, minVal) &&
check(node->right, maxVal, node->val);
}
bool isValidBST(TreeNode* root) {
if (root == nullptr)
return true;
return check(root, LONG_MAX, LONG_MIN);
}
};
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