Validate Binary Search Tree
描述
Given a binary tree, determine if it is a valid binary search tree (BST).
Assume a BST is defined as follows:
- The left subtree of a node contains only nodes with keys less than the node's key.
- The right subtree of a node contains only nodes with keys greater than the node's key.
- Both the left and right subtrees must also be binary search trees.
分析
无
代码
// Validate Binary Search Tree
// 时间复杂度O(n),空间复杂度O(\logn)
class Solution {
public:
bool isValidBST(TreeNode* root) {
return isValidBST(root, LONG_MIN, LONG_MAX);
}
bool isValidBST(TreeNode* root, long long lower, long long upper) {
if (root == nullptr) return true;
return root->val > lower && root->val < upper
&& isValidBST(root->left, lower, root->val)
&& isValidBST(root->right, root->val, upper);
}
};