Given the root of a binary tree, return true if it's symmetric around its center: its left half is a mirror image of its right half.
Trees are written level by level, with null for a missing child.
Examples
Example 1
- Input
- root = [1, 2, 2, 3, 4, 4, 3]
- Output
- true
Example 2
- Input
- root = [1, 2, 2, null, 3, null, 3]
- Output
- false
Constraints
- The tree has between
1and1000nodes. -100 <= Node.val <= 100