leetcode

0 class Solution {

1 public:

2 TreeNode *bstFromPreorder(vector<int> &preorder) {

3 int index = 0;

4 TreeNode *root = new TreeNode(preorder[index++]);

5 stack<TreeNode *> st;

6 st.push(root);

7 while (index < preorder.size()) {

8 int val = preorder[index++];

9 if (val < st.top()->val) {

10 st.push(st.top()->left = new TreeNode(val));

11 } else {

12 TreeNode *crnt = nullptr;

13 while (!st.empty() && val > st.top()->val)

14 crnt = st.top(), st.pop();

15 st.push(crnt->right = new TreeNode(val));

16 }

17 }

18 return root;

19 }

20 };