doll.cpp: In function 'void build(int, std::vector<int>)':
doll.cpp:11:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
11 | for (int i = 0; i<now.size(); i++)sep[i&1].push_back(now[i]);
| ~^~~~~~~~~~~
/usr/bin/ld: /tmp/ccWPjmaB.o: in function `main':
grader.cpp:(.text.startup+0x168): undefined reference to `create_circuit(int, std::vector<int, std::allocator<int> >)'
collect2: error: ld returned 1 exit status