leetcode

0 class Solution {

1 string preorder(TreeNode *root, bool left) {

2 if (!root) return "";

3

4 string res;

5 stack<TreeNode *> st;

6 st.push(root);

7 while (!st.empty()) {

8 TreeNode *root = st.top();

9 st.pop();

10 if (!root) {

11 res += "-";

12 continue;

13 }

14 res += root->val;

15 if (left) {

16 st.push(root->right);

17 st.push(root->left);

18 } else {

19 st.push(root->left);

20 st.push(root->right);

21 }

22 }

23 return res;

24 }

25

26 public:

27 bool isSymmetric(TreeNode *root) {

28 if (!root) return false;

29

30 return preorder(root->left, true) == preorder(root->right, false);

31 }

32 };