foo.cc: In function 'int main()':
foo.cc:37:12: warning: 'P.Problem::head' may be used uninitialized in this function [-Wmaybe-uninitialized]
   37 |   p2->next = head;
      |   ~~~~~~~~~^~~~~~
foo.cc:79:10: note: 'P.Problem::head' was declared here
   79 |  Problem P(n, k);
      |          ^

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