Symmetric Tree

   // Start typing your Java solution below
        // DO NOT write main() function
        if(root == null || root.left==null && root.right==null) return true;
       
        if(root.left!=null && root.right!=null){
            if(root.left.val == root.right.val){
                return checkTree(root.left.right, root.right.left) &&
                checkTree(root.left.left, root.right.right);
            }
        }
        return false;       
    }
   
    boolean checkTree(TreeNode first, TreeNode second){
        if(first==null && second ==null) return true;
        if(first==null || second == null) return false;
        if(first.val !=second.val) return false;
       
        return checkTree(first.left, second.right) &&
               checkTree(first.right, second.left);
    }