foo.cc: In function 'void solve()':
foo.cc:31:20: error: 'cal' was not declared in this scope
   31 |                 if(cal(a[i], a[j]) < minv)
      |                    ^~~
foo.cc:40:47: error: 'cal' was not declared in this scope
   40 |         b[a[loc1].index] = b[a[loc2].index] = cal(a[loc1], a[loc2]);
      |                                               ^~~

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