Store clause counter value from satcheck_minisat instead of storing the clause itself

Add comment to explain solver_clause_num + 1 in solver hardness, change <int> to <size_t>

Author: Natasha Yogananda Jeppu

src/solvers/solver_hardness.cpp

@@ -108,6 +108,8 @@ void solver_hardnesst::register_clause(
   std::cout << "0\n";
 #endif
 
+  // The clause_counter is incremented after the call to register_clause.
+  // Here we add 1 to solver_clause_num to incorporate this increment.
   current_hardness.clause_set.push_back(solver_clause_num + 1);
   std::sort(
     current_hardness.clause_set.begin(), current_hardness.clause_set.end());

src/solvers/solver_hardness.h

@@ -50,7 +50,7 @@ struct solver_hardnesst
     size_t clauses = 0;
     size_t literals = 0;
     std::unordered_set<size_t> variables = {};
-    std::vector<int> clause_set = {};
+    std::vector<size_t> clause_set = {};
 
     sat_hardnesst &operator+=(const sat_hardnesst &other);
   };