101. Symmetric Tree

 1 class Solution {
 2     StringBuilder sb1 = new StringBuilder();
 3     StringBuilder sb2 = new StringBuilder();
 4     public boolean isSymmetric(TreeNode root) {
 5         if(root == null) return true;
 6         leftR(root);
 7         rightR(root);
 8         if(sb1.toString().equals(sb2.toString())) {
 9             return true;
10         }else {
11             return false;
12         }
13         
14     }
15    
16     public void leftR(TreeNode root) {
17         if(root != null) {
18             leftR(root.left);
19             sb1.append("l");
20             sb1.append(root.val);
21             leftR(root.right);
22             sb1.append("r");
23         }
24             
25         
26  }
27     
28     public void rightR(TreeNode root) {
29         if(root != null) {
30             rightR(root.right);
31             sb2.append("r");
32             sb2.append(root.val);
33             rightR(root.left);
34             sb2.append("l");
35         }
36     }   
37 }