foo.cc: In function 'int main()':
foo.cc:24:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   24 |  for (int i = 0; i < a.size(); i++) {
      |                  ~~^~~~~~~~~~
foo.cc:25:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   25 |   for (int j = i; j < a.size(); j++) {
      |                   ~~^~~~~~~~~~

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