/in/foo.cc: In function 'int countPairsWithSum(const std::vector<int>&, 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 = 0; i < x.size(); ++i) {
      |                     ~~^~~~~~~~~~