# code/leetcode/v1/symmetric

# Symmetric Tree

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree [1,2,2,3,4,4,3] is symmetric:

1

/ \

2 2

/ \ / \

3 4 4 3

But the following [1,2,2,null,3,null,3] is not:

1

/ \

2 2

\ \

3 3

Note:

Bonus points if you could solve it both recursively and iteratively.

1 | public class Symmetric { |

The base case is that `if (root == null)`

.

First divide the problem into smallest piece that we judge the node’s value equals or not.

Then we conquer the problem that the node `left.left`

equals `right.right`

and `left.right`

equals `right.left`

.

Reference

https://leetcode-cn.com/problems/symmetric-tree/submissions