leetcode

0 class Solution {

1 public:

2 bool isValidBST(TreeNode *root) {

3 stack<TreeNode *> st;

4 long prev = LONG_MIN;

5 while (true) {

6 while (root) {

7 st.push(root);

8 root = root->left;

9 }

10 if (st.empty()) break;

11 root = st.top();

12 st.pop();

13 if (root->val <= prev) return false;

14 prev = root->val;

15 root = root->right;

16 }

17 return true;

18 }

19 };