bool validBST(TreeNode *root, int minVal, int maxVal)
{
if (root == NULL)
return true;
if (!(root->val > minVal && root->val < maxVal))
return false;
return validBST(root->left, minVal, root->val) && validBST(root->right, root->val, maxVal);
}
bool validBST(TreeNode *root, bool minBound, int min, bool maxBound, int max) {
if (root == NULL)
return true;
if (minBound && min >= root->val)
return false;
if (maxBound && max <= root->val)
return false;
return validBST(root->left, minBound, min, true, root->val)
&& validBST(root->right, true, root->val, maxBound, max);
}
bool validBST(TreeNode* root, int& minVal, int& maxVal) {
minVal = maxVal = root->val;
int tmpMinVal, tmpMaxVal;
if (root->left != NULL) {
bool left = validBST(root->left, tmpMinVal, tmpMaxVal);
if (left == false || tmpMaxVal >= root->val)
return false;
minVal = min(minVal, tmpMinVal);
}
if (root->right != NULL) {
bool right = validBST(root->right, tmpMinVal, tmpMaxVal);
if (right == false || tmpMinVal <= root->val)
return false;
maxVal = max(maxVal, tmpMaxVal);
}
return true;
}
bool isValidBST(TreeNode *root) {
return validBST(root, false, 0, false, 0);
}
bool isValidBST(TreeNode *root) {
return validBST(root, INT_MIN, INT_MAX);
}
bool isValidBST(TreeNode* root) {
if (root == NULL) return true;
int minVal, maxVal;
return validBST(root, minVal, maxVal);
}
