Language: C++

#include <bits/stdc++.h>
using namespace std;

int main(){
  int n,m;
  cin>>n>>m;
  set<set<int>> f;
  set<int> result;
  int a,b;
  for(int i=0;i<m;i++){
    cin>>a>>b;
    f.insert({a,b});
  }
  int max=1;
  bool add=true;
  while((int)f.size()>0){
    if(add){
      if((int)result.size()>max){
        max=result.size();
      }
      result={(*(*f.begin()).begin()),(*(*f.begin()).begin()+1)};
      f.erase(f.begin());
    }
    if(f.size()==0){
      break;
    }
    add=true;
    for(int i=0;i<(int)f.size();i++){
      if(result.count((*(*f.begin()).begin()))){
        result.insert((*(*f.begin()).begin()+1));
        add=false;
        f.erase(f.begin()+i);
        i--;
      }else if(result.count((*(*f.begin()).begin()+1))){
        result.insert((*(*f.begin()).begin()));
        add=false;
        f.erase(f.begin()+i);
        i--;
      }
    }
  }
  if(result.size()>max){
    max=result.size();
  }
  cout<<max<<endl;
}
    
  




Compiler output:
a.cc: In function 'int main()':
a.cc:32:26: error: no match for 'operator+' (operand types are 'std::set<std::set<int> >::iterator' {aka 'std::_Rb_tree<std::set<int>, std::set<int>, std::_Identity<std::set<int> >, std::less<std::set<int> >, std::allocator<std::set<int> > >::const_iterator'} and 'int')
   32 |         f.erase(f.begin()+i);
      |                 ~~~~~~~~~^~
      |                        |  |
      |                        |  int
      |                        std::set<std::set<int> >::iterator {aka std::_Rb_tree<std::set<int>, std::set<int>, std::_Identity<std::set<int> >, std::less<std::set<int> >, std::allocator<std::set<int> > >::const_iterator}
In file included from /usr/include/c++/14/bits/stl_algobase.h:67,
                 from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_iterator.h:627:5: note: candidate: 'template<class _Iterator> constexpr std::reverse_iterator<_Iterator> std::operator+(typename reverse_iterator<_Iterator>::difference_type, const reverse_iterator<_Iterator>&)'
  627 |     operator+(typename reverse_iterator<_Iterator>::difference_type __n,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:627:5: note:   template argument deduction/substitution failed:
a.cc:32:27: note:   mismatched types 'const std::reverse_iterator<_Iterator>' and 'int'
   32 |         f.erase(f.begin()+i);
      |                           ^
/usr/include/c++/14/bits/stl_iterator.h:1798:5: note: candidate: 'template<class _Iterator> constexpr std::move_iterator<_IteratorL> std::operator+(typename move_iterator<_IteratorL>::difference_type, const move_iterator<_IteratorL>&)'
 1798 |     operator+(typename move_iterator<_Iterator>::difference_type __n,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1798:5: note:   template argument deduction/substitution failed:
a.cc:32:27: note:   mismatched types 'const std::move_iterator<_IteratorL>' and 'int'
   32 |         f.erase(f.begin()+i);
      |                           ^
In file included from /usr/include/c++/14/string:54,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52:
/usr/include/c++/14/bits/basic_string.h:3598:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3598 |     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3598:5: note:   template argument deduction/substitution failed:
a.cc:32:27: note:   'std::set<std::set<int> >::iterator' {aka 'std::_Rb_tree<std::set<int>, std::set<int>, std::_Identity<std::set<int> >, std::less<std::set<int> >, std::allocator<std::set<int> > >::const_iterator'} is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   32 |         f.erase(f.begin()+i);
      |                           ^
/usr/include/c++/14/bits/basic_string.h:3616:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const _CharT*, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3616 |     operator+(const _CharT* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3616:5: note:   template argument deduction/substitution failed:
a.cc:32:27: note:   mismatched types 'const _CharT*' and 'std::_Rb_tree_const_iterator<std::set<int> >'
   32 |         f.erase(f.begin()+i);
      |                           ^
/usr/include/c++/14/bits/basic_string.h:3635:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(_CharT, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3635 |     operator+(_CharT __lhs, const basic_string<_CharT,_Traits,_Alloc>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3635:5: note:   template argument deduction/substitution failed:
a.cc:32:27: note:   mismatched types 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>' and 'int'
   32 |         f.erase(f.begin()+i);
      |                           ^
/usr/include/c++/14/bits/basic_string.h:3652:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*)'
 3652 |     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3652:5: note:   template argument deduction/substitution failed:
a.cc:32:27: note:   'std::set<std::set<int> >::iterator' {aka 'std::_Rb_tree<std::set<int>, std::set<int>, std::_Identity<std::set<int> >, std::less<std::set<int> >, std::allocator<std::set<int> > >::const_iterator'} is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   32 |         f.erase(f.begin()+i);
      |                           ^
/usr/include/c++/14/bits/basic_string.h:3670:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, _CharT)'
 3670 |     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs, _CharT __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3670:5: note:   template argument deduction/substitution failed:
a.cc:32:27: note:   'std::set<std::set<int> >::iterator' {aka 'std::_Rb_tree<std::set<int>, std::set<int>, std::_Identity<std::set<int> >, std::less<std::set<int> >, std::allocator<std::set<int> > >::const_iterator'} is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   32 |         f.erase(f.begin()+i);
      |                           ^
/usr/include/c++/14/bits/basic_string.h:3682:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(__cxx11::basic_string<_CharT, _Traits, _Allocator>&&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3682 |     operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3682:5: note:   template argument deduction/substitution failed:
a.cc:32:27: note:   'std::set<std::set<int> >::iterator' {aka 'std::_Rb_tree<std::set<int>, std::set<int>, std::_Identity<std::set<int> >, std::less<std::set<int> >, std::allocator<std::set<int> > >::const_iterator'} is not derived from 'std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   32 |         f.erase(f.begin()+i);
      |                           ^
/usr/include/c++/14/bits/basic_string.h:3689:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, __cxx11::basic_string<_CharT, _Traits, _Allocator>&&)'
 3689 |     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3689:5: note:   template argument deduction/substitution failed:
a.cc:32:27: note:   'std::set<std::set<int> >::iterator' {aka 'std::_Rb_tree<std::set<int>, std::set<int>, std::_Identity<std::set<int> >, std::less<std::set<int> >, std::allocator<std::set<int> > >::const_iterator'} is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   32 |         f.erase(f.begin()+i);
      |                           ^
/usr/include/c++/14/bits/basic_string.h:3696:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(__cxx11::basic_string<_CharT, _Traits, _Allocator>&&, __cxx11::basic_string<_CharT, _Traits, _Allocator>&&)'
 3696 |     operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3696:5: note:   template argument deduction/substitution failed:
a.cc:32:27: note:   'std::set<std::set<int> >::iterator' {aka 'std::_Rb_tree<std::set<int>, std::set<int>, std::_Identity<std::set<int> >, std::less<std::set<int> >, std::allocator<std::set<int> > >::const_iterator'} is not derived from 'std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   32 |         f.erase(f.begin()+i);
      |                           ^
/usr/include/c++/14/bits/basic_string.h:3719:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const _CharT*, __cxx11::basic_string<_CharT, _Traits, _Allocator>&&)'
 3719 |     operator+(const _CharT* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3719:5: note:   template argument deduction/substitution failed:
a.cc:32:27: note:   mismatched types 'const _CharT*' and 'std::_Rb_tree_const_iterator<std::set<int> >'
   32 |         f.erase(f.begin()+i);
      |                           ^
/usr/include/c++/14/bits/basic_string.h:3726:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(_CharT, __cxx11::basic_string<_CharT, _Traits, _Allocator>&&)'
 3726 |     operator+(_CharT __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3726:5: note:   template argument deduction/substitution failed:
a.cc:32:27: note:   mismatched types 'std::__cxx11::basic_string<_CharT, _Traits, _Allocator>' and 'int'
   32 |         f.erase(f.begin()+i);
      |                           ^
/usr/include/c++/14/bits/basic_string.h:3733:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(__cxx11::basic_string<_CharT, _Traits, _Allocator>&&, const _CharT*)'
 3733 |     operator+(basic_string<_CharT, _Tra