# Symmetric Tree

## Description

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
```

**Follow up:** Solve it both recursively and iteratively.

## **Code**

```java
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean isSymmetric(TreeNode root) {
        return root == null || isSymmetricHelper(root.left, root.right);
        
    }
    
    public boolean isSymmetricHelper(TreeNode left, TreeNode right) {
        if (left == null || right == null) return left == right;
        if (left.val != right.val) return false;
        return isSymmetricHelper(left.left, right.right) && isSymmetricHelper(left.right, right.left);
    }
}
```
