answer.code: In function ‘void construct_two_trees(int, std::vector<int>, std::vector<int>)’:
answer.code:100:19: error: cannot convert ‘<brace-enclosed initializer list>’ to ‘int’
  100 |         add_vertex({x, (x + 1) % n, (x + 2) % n});
      |         ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |                   |
      |                   <brace-enclosed initializer list>
In file included from answer.code:1:
island.h:6:20: note:   initializing argument 1 of ‘int add_vertex(int, int, int)’
    6 | int add_vertex(int i, int j, int k);
      |                ~~~~^