leetcode

0 class Solution {

1 public:

2 TreeNode *bstToGst(TreeNode *root) {

3 TreeNode *head = root;

4 stack<TreeNode *> st;

5 int sum = 0;

6 while (true) {

7 while (root) {

8 st.push(root);

9 root = root->right;

10 }

11 if (st.empty()) break;

12 root = st.top(), st.pop();

13 sum = root->val += sum;

14 root = root->left;

15 }

16 return head;

17 }

18 };