/usr/bin/ld: /tmp/ccUNpcTH.o: in function `main':
grader.cpp:(.text.startup+0x0): multiple definition of `main'; /tmp/ccsWLJ0I.o:roads.cpp:(.text.startup+0x0): first defined here
/usr/bin/ld: /tmp/ccsWLJ0I.o: in function `main':
roads.cpp:(.text.startup+0x13e): undefined reference to `minimum_closure_costs(int, std::vector<int, std::allocator<int> >, std::vector<int, std::allocator<int> >, std::vector<int, std::allocator<int> >)'
/usr/bin/ld: /tmp/ccUNpcTH.o: in function `main':
grader.cpp:(.text.startup+0x26f): undefined reference to `minimum_closure_costs(int, std::vector<int, std::allocator<int> >, std::vector<int, std::allocator<int> >, std::vector<int, std::allocator<int> >)'
collect2: error: ld returned 1 exit status