answer.code: In function ‘std::vector<std::vector<int> > gen(int)’:
answer.code:315:38: error: could not convert ‘mem.std::vector<std::vector<int> >::operator[](((std::vector<std::vector<int> >::size_type)n))’ from ‘vector<int>’ to ‘vector<std::vector<int>>’
  315 |     if (!mem[n].empty()) return mem[n];
      |                                      ^
      |                                      |
      |                                      vector<int>
answer.code:318:25: error: no match for ‘operator=’ (operand types are ‘__gnu_cxx::__alloc_traits<std::allocator<std::vector<int> >, std::vector<int> >::value_type’ {aka ‘std::vector<int>’} and ‘std::vector<std::vector<int> >’)
  318 |         return mem[n] = all;
      |                         ^~~
In file included from /usr/include/c++/11/vector:72,
                 from answer.code:16:
/usr/include/c++/11/bits/vector.tcc:198:5: note: candidate: ‘std::vector<_Tp, _Alloc>& std::vector<_Tp, _Alloc>::operator=(const std::vector<_Tp, _Alloc>&) [with _Tp = int; _Alloc = std::allocator<int>]’
  198 |     vector<_Tp, _Alloc>::
      |     ^~~~~~~~~~~~~~~~~~~
/usr/include/c++/11/bits/vector.tcc:199:42: note:   no known conversion for argument 1 from ‘std::vector<std::vector<int> >’ to ‘const std::vector<int>&’
  199 |     operator=(const vector<_Tp, _Alloc>& __x)
      |               ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
In file included from /usr/include/c++/11/vector:67,
                 from answer.code:16:
/usr/include/c++/11/bits/stl_vector.h:709:7: note: candidate: ‘std::vector<_Tp, _Alloc>& std::vector<_Tp, _Alloc>::operator=(std::vector<_Tp, _Alloc>&&) [with _Tp = int; _Alloc = std::allocator<int>]’
  709 |       operator=(vector&& __x) noexcept(_Alloc_traits::_S_nothrow_move())
      |       ^~~~~~~~
/usr/include/c++/11/bits/stl_vector.h:709:26: note:   no known conversion for argument 1 from ‘std::vector<std::vector<int> >’ to ‘std::vector<int>&&’
  709 |       operator=(vector&& __x) noexcept(_Alloc_traits::_S_nothrow_move())
      |                 ~~~~~~~~~^~~
/usr/include/c++/11/bits/stl_vector.h:730:7: note: candidate: ‘std::vector<_Tp, _Alloc>& std::vector<_Tp, _Alloc>::operator=(std::initializer_list<_Tp>) [with _Tp = int; _Alloc = std::allocator<int>]’
  730 |       operator=(initializer_list<value_type> __l)
      |       ^~~~~~~~
/usr/include/c++/11/bits/stl_vector.h:730:46: note:   no known conversion for argument 1 from ‘std::vector<std::vector<int> >’ to ‘std::initializer_list<int>’
  730 |       operator=(initializer_list<value_type> __l)
      |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
answer.code: In function ‘void fast_scan(int&)’:
answer.code:105:31: warning: ignoring return value of ‘int scanf(const char*, ...)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
  105 | void fast_scan(int &x) { scanf("%d", &x); }
      |                          ~~~~~^~~~~~~~~~
answer.code: In function ‘void fast_scan(long long int&)’:
answer.code:106:37: warning: ignoring return value of ‘int scanf(const char*, ...)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
  106 | void fast_scan(long long &x) { scanf("%lld", &x); }
      |                                ~~~~~^~~~~~~~~~~~
answer.code: In function ‘void fast_scan(long long unsigned int&)’:
answer.code:107:46: warning: ignoring return value of ‘int scanf(const char*, ...)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
  107 | void fast_scan(unsigned long long &x) { scanf("%llu", &x); }
      |                                         ~~~~~^~~~~~~~~~~~
answer.code: In function ‘void fast_scan(double&)’:
answer.code:108:34: warning: ignoring return value of ‘int scanf(const char*, ...)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
  108 | void fast_scan(double &x) { scanf("%lf", &x); }
      |                             ~~~~~^~~~~~~~~~~
answer.code: In function ‘void fast_scan(long double&)’:
answer.code:109:39: warning: ignoring return value of ‘int scanf(const char*, ...)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
  109 | void fast_scan(long double &x) { scanf("%Lf", &x); }
      |                                  ~~~~~^~~~~~~~~~~
answer.code: In function ‘void fast_scan(char&)’:
answer.code:111:14: warning: ignoring return value of ‘int scanf(const char*, ...)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
  111 |         scanf("%c", &x);
      |         ~~~~~^~~~~~~~~~
answer.code: In function ‘void fast_scan(std::string&)’:
answer.code:117:14: warning: ignoring return value of ‘int scanf(const char*, ...)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
  117 |         scanf("%s", string_in_buffer);
      |         ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~