In file included from /usr/include/c++/11/unordered_map:35,
                 from answer.code:11:
/usr/include/c++/11/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
   32 | #error This file requires compiler and library support \
      |  ^~~~~
answer.code: In function ‘int main()’:
answer.code:29:13: error: ‘nullptr’ was not declared in this scope
   29 |     cin.tie(nullptr);
      |             ^~~~~~~
answer.code:43:21: warning: range-based ‘for’ loops only available with ‘-std=c++11’ or ‘-std=gnu++11’
   43 |         for(int c : adj[a]) { //c = set of a's adj nodes (opposite side as a)
      |                     ^~~
answer.code:43:26: error: forming reference to reference type ‘std::vector<int>&’
   43 |         for(int c : adj[a]) { //c = set of a's adj nodes (opposite side as a)
      |                          ^
answer.code:44:25: warning: range-based ‘for’ loops only available with ‘-std=c++11’ or ‘-std=gnu++11’
   44 |             for(int b : adj[c]) { //b = set of c's adj nodes (same side as a)
      |                         ^~~
answer.code:44:30: error: forming reference to reference type ‘std::vector<int>&’
   44 |             for(int b : adj[c]) { //b = set of c's adj nodes (same side as a)
      |                              ^