 # [LeetCode] Symmetric Tree

## Problem

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

### Example

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.

## Solution

### Recursion

``````class Solution {
public boolean isSymmetric(TreeNode root) {
if (root == null) return true;
return dfs(root.left, root.right);
}
private boolean dfs(TreeNode left, TreeNode right) {
if (left == null) return right == null;
if (right == null) return left == null;
if (left.val != right.val) {
return false;
}
return dfs(left.left, right.right) && dfs(left.right, right.left);
}
}``````

### Iteration

``````class Solution {
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) return false;
if (left == null && right == null) continue;
if (left.val != right.val) return false;
queue.offer(left.left);
queue.offer(right.right);
queue.offer(left.right);
queue.offer(right.left);
}
return true;
}
}``````