class TreeNode {
     int val;
     TreeNode left;
     TreeNode right;
     TreeNode(int x) { val = x; }
 }
public class Solution {

    //判斷一棵樹是否為對稱二叉樹
    public boolean isSymmetric(TreeNode root) {
        if(root==null||(root.left==null&&root.right==null))
            return true;

        return
 
 isSymmetricCheck(root,root);
    }
    //遞迴呼叫實現
    public boolean isSymmetricCheck(TreeNode x,TreeNode y){

          if(x==null&&y==null) return true;
          if((x!=null&&y==null)||(x==null&&y!=null)) return false;

          return (x.val==y.val)&&isSymmetricCheck(x.left,y.right)&&isSymmetricCheck(x.right,y.left);
    }

    public
 
 static void main(String[]args){
       //System.out.println("Hello Wolrd!");
       TreeNode root=new TreeNode(1);
       root.left=new TreeNode(2);
       root.right=new TreeNode(2);
       root.left.left=new TreeNode(3);
       root.right.right=new TreeNode(3);
       Solution s=new Solution();
       System.out
 
.println(s.isSymmetric(root));

    }
}