## 题目：https://www.nowcoder.com/practice/1b0b7f371eae4204bc4a7570c84c2de1

• 题解：这道题需要注意的地方就是对称的意思的理解，当root的左右孩子left和right的数值相等，同时left.left和right.right以及left.right和right.left分别对应对称时，root是对称的。这道题可以使用递归和迭代（使用队列）来做，具体可参见代码

• java代码实现：

```import java.util.*;
public class Solution {
/**
*
* @param root TreeNode类
* @return bool布尔型
*/
public boolean isSymmetric (TreeNode root) {
if(root == null)
return true;
return check(root.left, root.right);
}

//递归
public boolean check(TreeNode left, TreeNode right){
if(left == null && right == null)
return true;
if(left == null || right == null)
return false;
return left.val == right.val && check(left.left, right.right) && check(left.right, right.left);
}

//迭代
public boolean isSymmetric (TreeNode root) {
if(root == null)
return true;
queue.offer(root.left);
queue.offer(root.right);
while(!queue.isEmpty()){
TreeNode left = queue.poll();
TreeNode right = queue.poll();
if(left == null && right == null)
continue;
if(left == null || right == null || left.val != right.val)
return false;
queue.offer(left.left);
queue.offer(right.right);
queue.offer(left.right);
queue.offer(right.left);
}
return true;
}
}```