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/**
* 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 isValidBSTRec(TreeNode* root, int* min, int* max) {
if (root->left && root->right) {
int leftMin, leftMax, rightMin, rightMax;
if (!isValidBSTRec(root->left, &leftMin, &leftMax) ||
!isValidBSTRec(root->right, &rightMin, &rightMax)) {
return false;
}
*min = std::min(std::min(leftMin, rightMin), root->val);
*max = std::max(std::max(leftMax, rightMax), root->val);
return (leftMax < root->val) && (root->val < rightMin);
}
else if (root->left) {
int leftMin, leftMax;
if (!isValidBSTRec(root->left, &leftMin, &leftMax)) {
return false;
}
*min = std::min(leftMin, root->val);
*max = std::max(leftMax, root->val);
return (leftMax < root->val);
}
else if (root->right) {
int rightMin, rightMax;
if (!isValidBSTRec(root->right, &rightMin, &rightMax)) {
return false;
}
*min = std::min(rightMin, root->val);
*max = std::max(rightMax, root->val);
return (root->val < rightMin);
}
else {
*min = *max = root->val;
return true;
}
}
bool isValidBST(TreeNode* root) {
if (!root) return true;
int minVal, maxVal;
return isValidBSTRec(root, &minVal, &maxVal);
}
};
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