I Don't Want to Hire You If You Can't Reverse a Binary Tree (2016) (thecodebarbarian.com)

Everything about the way we hire is so silly.

I don't think this hiring methodology is good. Just look at all of the negative comments on the post itself! Many of them make good points.

Just traverse the tree forwards and backwards simultaneously and match the moves. I hate peevish interviewers. If you want to show off, write a paper.

  bool is_mirror(left_tree,right_tree) {

    if( !left_tree && !right_tree)
      return true;

    if( !left_tree || !right_tree)
      return false;

    return is_mirror(left_tree->left, right_tree->right)
      && is_mirror(left_tree->right, right_tree->left);

    }

  bool is_symmetric(tree) {
    !tree || is_mirror(tree-left,tree->right);
  }