Java determines whether a number is symmetric

Title description

Given a binary tree, judge whether Qi is a mirror image of itself (that is, whether it is symmetrical).
For example: the following binary tree is symmetric
     1
    / \
  2 2
 / \ / \
3 4 4 3
The following binary tree is asymmetric.
    1
    / \
  2 2
    \ \
    3 3
Note:
I hope you can use recursion and iteration to solve this problem

Example 1

enter

{1,2,2}

return value

true

 

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 * }
 */

public class Solution {
    
    /**
     * 
     * @param root TreeNode类 
     * @return bool布尔型
     */
    public boolean isSymmetric (TreeNode root) {
       
        return preTree(root,root);
    }
    
    public boolean preTree(TreeNode tree1,TreeNode tree2){
        
        if(tree1==null && tree2==null){
            return true;
        }       
        
        if(tree1==null || tree2==null){
            return false;
        }
        
        if(tree1.val != tree2.val){
            return false;
        }
        
        return preTree(tree1.left,tree2.right) && preTree(tree1.right,tree2.left);
    }
}