leetcode -- Symmetric Tree

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.

recursive method

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