/in/foo.cc: In function 'bool canFormArithmeticSequence(std::vector<int>&)':
/in/foo.cc:9:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    9 |     for (int i = 1; i < cards.size() - 1; ++i) {
      |                     ~~^~~~~~~~~~~~~~~~~~