101. Symmetric Tree

 1     public boolean isSymmetric(TreeNode root) {
 2         return isSameTree(root, root);
 3     }
 4     
 5     private boolean isSameTree(TreeNode p, TreeNode q) {
 6         if(p == null && q == null) {
 7             return true;
 8         }
 9         if(p == null || q == null) {
10             return false;
11         }
12         if(p.val != q.val) {
13             return false;
14         }
15         return isSameTree(p.left, q.right) && isSameTree(p.right, q.left);
16     }