Time Cost

23min24s

Code

/**
 * 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 isValidBST(TreeNode* root) {
        return isBST(root, 
            -1*pow(2,31)-1, 
            pow(2,31));
    }

    bool isBST(TreeNode* current, long minn, long maxx) {
        if (current == nullptr) return true;

        if (minn >= current->val || maxx <= current->val) {
            return false;
        }

        return isBST(current->left, minn, current->val) && isBST(current->right, current->val, maxx);
    }
};