101. 对称二叉树

 1 public class SymmetricTree {
 2     static class TreeNode {
 3         int val;
 4         TreeNode left;
 5         TreeNode right;
 6         TreeNode(int x) {
 7             val = x;
 8         }
 9     }
10     
11     public boolean isSymmetric(TreeNode root) {
12         if(root == null) {
13             return true;
14         }
15         return isSameTree(root.left, root.right);
16     }
17     
18     public  static boolean isSameTree(TreeNode root1, TreeNode root2) {
19         if(root1 == null && root2 == null) {
20             return true;
21         }
22         if(root1 == null || root2 == null) {
23             return false;    
24         }
25         if(root1.val != root2.val) {
26             return false;
27         }
28         return isSameTree(root1.left, root2.right) && isSameTree(root1.right, root2.left);
29     }
30 }