Normal: https://abc070.contest.atcoder.jp/ Beta: https://beta.atcoder.jp/contests/abc070

My first solution for D (which use recursive DFS) got RE, so I had to rewrite a non-recursive DFS solution in order to get AC. Is it because of the low stack size limit for Python?

A bit unrelated, but I want to ask Python user how do you deal with problems that require Balanced BST? There is nothing similar to set, map in C++, and it's definitely not a good idea to re-invent the entire thing under the constrained time of the contest.

The editorial defines a struct instead of make_pair():

using edge = struct { int to; ll cost;};
vector<edge> tree[limit];

The main benefit I see is that you can reference the components by meaningful name like ".cost" instead of ".second".

Is there any other benefit?

p.s. That new syntax of "using" versus "typedef" is also cool.