bool isValidBSTHelper(TreeNode *root, int low, int high){
if (!root) return true;
if (root->val <= low || root->val >= high) return false;
return isValidBSTHelper(root->left, low, root->val) && isValidBSTHelper(root->right, root->val, high);
}
bool isValidBSTHelper( TreeNode *root, int min, int max )
{
if( root == NULL ) return true;
return (root->val>min&&root->val<max)
&&isValidBSTHelper( root->left, min, root->val )
&&isValidBSTHelper( root->right, root->val, max );
}
bool isValidBSTHelper(TreeNode *node, TreeNode* &min) {
if (!node) return true;
if (node->left && !isValidBSTHelper(node->left, min)) return false;
if (min && node->val <= min->val) return false;
min = node;
if (node->right && !isValidBSTHelper(node->right, min)) return false;
return true;
}
bool isValidBSTHelper(TreeNode* root, long min, long max){
if(!root){
return true;
}
if((root->val >= max) || (root->val <= min)){
return false;
}
return isValidBSTHelper(root->left, min, root->val) && isValidBSTHelper(root->right, root->val, max);
}
bool isValidBSTHelper(TreeNode* node, int &prev) {
if (node == NULL) return true;
if (isValidBSTHelper(node->left, prev)) {
if (prev < node->val) {
prev = node->val;
return isValidBSTHelper(node->right, prev);
}
return false;
}
return false;
}
bool isValidBSTHelper(TreeNode* root, int min, int max) {
if(root == NULL) {
return true;
}
if(root->val <= min || root->val >= max) { // 这里是否取等号可以和下面的isValidBSTHelper的第一个参数结合起来考虑
return false;
}
bool left = isValidBSTHelper(root->left, min, root->val);
bool right = isValidBSTHelper(root->right, root->val, max);
return left && right;
}
bool isValidBST(TreeNode *root) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
if( root == NULL ) return true;
int min = -100000;
int max = 100000;
return isValidBSTHelper( root, min, max );
}
bool isValidBST(TreeNode *root) {
// IMPORTANT: Please reset any member data you declared, as
// the same Solution instance will be reused for each test case.
return isValidBSTHelper(root, INT_MIN, INT_MAX);
}
bool isValidBST(TreeNode* root) {
return isValidBSTHelper(root, INT_MIN - 1L, INT_MAX + 1L);
}
// Inorder traversal (lower bound)
bool isValidBST(TreeNode *root) {
TreeNode* min = NULL;
return isValidBSTHelper(root, min);
}
bool isValidBSTHelper(TreeNode *node, TreeNode* min, TreeNode* max) {
if (!node) return true;
if ((min && node->val <= min->val) || (max && node->val >= max->val)) return false;
return isValidBSTHelper(node->left, min, node) &&
isValidBSTHelper(node->right, node, max);
}
bool isValidBST(TreeNode *root) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
int prev = INT_MIN;
return isValidBSTHelper(root, prev);
}
bool isValidBST(TreeNode *root) {
// Note: The Solution object is instantiated only once and is reused by each test case.
return isValidBSTHelper(root,INT_MIN,INT_MAX);
}