foo.cc: In function 'int main()':
foo.cc:33:25: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<Node>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   33 |         for(int i = 0;i < v[temp].size();i ++) {
      |                       ~~^~~~~~~~~~~~~~~~
foo.cc:49:20: warning: passing NULL to non-pointer argument 1 of 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]' [-Wconversion-null]
   49 |     if(flag) cout<<NULL;
      |                    ^~~~
In file included from /usr/include/c++/9/iostream:39,
                 from foo.cc:1:
/usr/include/c++/9/ostream:166:23: note:   declared here
  166 |       operator<<(long __n)
      |                  ~~~~~^~~

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