Language: C++

/*Function Template*/
#include<bits/stdc++.h>
using namespace std;
const int mod = 1000000007;
#define rep(i, n) for(int i = 0; i < (n); i++)


int Len(int n) {
  int s=0;
  while(n!=0) s++, n/=10;
  return s;
}


int Sint(int n) {
  int m=0,s=0,a=n;
  while(a!=0) s++, a/=10;
  for(int i=s-1;i>=0;i--) m+=n/((int)pow(10,i))-(n/((int)pow(10,i+1)))*10;
  return m;
}


int GCD(int a,int b)
{
  int r, tmp;
   /* 自然数 a > b を確認・入替 */
  if(a<b){
    tmp = a;
    a = b;
    b = tmp;
  }
  /* ユークリッドの互除法 */
  r = a % b;
  while(r!=0){
    a = b;
    b = r;
    r = a % b;
  }
  return b;
}


int Factorial(int n){
  int m=1;
  while(n>=1) m*=n,n--;
  return m;
}


long long int Svec(vector<long long int> v){
  long long int n=0;
  for(long long int i=0;i<v.size();i++) n+=v[i];
  return n;
}


/*↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓*/
int main() {
  int n,m;
  bool flag=false;
  cin>>n>>m;
  vector<pair<int,int>> v;
  set<int> st1,st2;
  rep(i,m){
    int a,b;
    cin>>a>>b;
    if(a==1 && b==n){
      cout<<"POSSIBLE"<<endl;
      return 0;
    }
    v.emplace_back(a,b);
  }
  rep(i,m){
    if(v[i].first==1){
      st1.insert(v[i].second);
    }
  }
  rep(i,m){
    if(v[i].second==n){
      st2.insert(v[i].first);
    }
  }
  if((st1 & st2).size()>=1) flag=true;
  if(flag){
    cout<<"POSSIBLE"<<endl;
  }else{
    cout<<"IMPOSSIBLE"<<endl;
  }
}

Compiler output:
a.cc: In function 'int main()':
a.cc:83:11: error: no match for 'operator&' (operand types are 'std::set<int>' and 'std::set<int>')
   83 |   if((st1 & st2).size()>=1) flag=true;
      |       ~~~ ^ ~~~
      |       |     |
      |       |     set<[...]>
      |       set<[...]>
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52,
                 from a.cc:2:
/usr/include/c++/14/bitset:1557:5: note: candidate: 'template<long unsigned int _Nb> std::bitset<_Nb> std::operator&(const bitset<_Nb>&, const bitset<_Nb>&)'
 1557 |     operator&(const bitset<_Nb>& __x, const bitset<_Nb>& __y) _GLIBCXX_NOEXCEPT
      |     ^~~~~~~~
/usr/include/c++/14/bitset:1557:5: note:   template argument deduction/substitution failed:
a.cc:83:13: note:   'std::set<int>' is not derived from 'const std::bitset<_Nb>'
   83 |   if((st1 & st2).size()>=1) flag=true;
      |             ^~~
In file included from /usr/include/c++/14/valarray:605,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:166:
/usr/include/c++/14/bits/valarray_after.h:411:5: note: candidate: 'template<class _Dom1, class _Dom2> std::_Expr<std::__detail::_BinClos<std::__bitwise_and, std::_Expr, std::_Expr, _Dom1, _Dom2>, typename std::__fun<std::__bitwise_and, typename _Dom1::value_type>::result_type> std::operator&(const _Expr<_Dom1, typename _Dom1::value_type>&, const _Expr<_Dom2, typename _Dom2::value_type>&)'
  411 |     _DEFINE_EXPR_BINARY_OPERATOR(&, struct std::__bitwise_and)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:411:5: note:   template argument deduction/substitution failed:
a.cc:83:13: note:   'std::set<int>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   83 |   if((st1 & st2).size()>=1) flag=true;
      |             ^~~
/usr/include/c++/14/bits/valarray_after.h:411:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__bitwise_and, std::_Expr, std::_Constant, _Dom, typename _Dom::value_type>, typename std::__fun<std::__bitwise_and, typename _Dom1::value_type>::result_type> std::operator&(const _Expr<_Dom1, typename _Dom1::value_type>&, const typename _Dom::value_type&)'
  411 |     _DEFINE_EXPR_BINARY_OPERATOR(&, struct std::__bitwise_and)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:411:5: note:   template argument deduction/substitution failed:
a.cc:83:13: note:   'std::set<int>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   83 |   if((st1 & st2).size()>=1) flag=true;
      |             ^~~
/usr/include/c++/14/bits/valarray_after.h:411:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__bitwise_and, std::_Constant, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__bitwise_and, typename _Dom1::value_type>::result_type> std::operator&(const typename _Dom::value_type&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  411 |     _DEFINE_EXPR_BINARY_OPERATOR(&, struct std::__bitwise_and)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:411:5: note:   template argument deduction/substitution failed:
a.cc:83:13: note:   'std::set<int>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   83 |   if((st1 & st2).size()>=1) flag=true;
      |             ^~~
/usr/include/c++/14/bits/valarray_after.h:411:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__bitwise_and, std::_Expr, std::_ValArray, _Dom, typename _Dom::value_type>, typename std::__fun<std::__bitwise_and, typename _Dom1::value_type>::result_type> std::operator&(const _Expr<_Dom1, typename _Dom1::value_type>&, const valarray<typename _Dom::value_type>&)'
  411 |     _DEFINE_EXPR_BINARY_OPERATOR(&, struct std::__bitwise_and)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:411:5: note:   template argument deduction/substitution failed:
a.cc:83:13: note:   'std::set<int>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   83 |   if((st1 & st2).size()>=1) flag=true;
      |             ^~~
/usr/include/c++/14/bits/valarray_after.h:411:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__bitwise_and, std::_ValArray, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__bitwise_and, typename _Dom1::value_type>::result_type> std::operator&(const valarray<typename _Dom::value_type>&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  411 |     _DEFINE_EXPR_BINARY_OPERATOR(&, struct std::__bitwise_and)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:411:5: note:   template argument deduction/substitution failed:
a.cc:83:13: note:   'std::set<int>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   83 |   if((st1 & st2).size()>=1) flag=true;
      |             ^~~
/usr/include/c++/14/valarray:1202:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__bitwise_and, std::_ValArray, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__bitwise_and, _Tp>::result_type> std::operator&(const valarray<_Tp>&, const valarray<_Tp>&)'
 1202 | _DEFINE_BINARY_OPERATOR(&, __bitwise_and)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1202:1: note:   template argument deduction/substitution failed:
a.cc:83:13: note:   'std::set<int>' is not derived from 'const std::valarray<_Tp>'
   83 |   if((st1 & st2).size()>=1) flag=true;
      |             ^~~
/usr/include/c++/14/valarray:1202:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__bitwise_and, std::_ValArray, std::_Constant, _Tp, _Tp>, typename std::__fun<std::__bitwise_and, _Tp>::result_type> std::operator&(const valarray<_Tp>&, const typename valarray<_Tp>::value_type&)'
 1202 | _DEFINE_BINARY_OPERATOR(&, __bitwise_and)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1202:1: note:   template argument deduction/substitution failed:
a.cc:83:13: note:   'std::set<int>' is not derived from 'const std::valarray<_Tp>'
   83 |   if((st1 & st2).size()>=1) flag=true;
      |             ^~~
/usr/include/c++/14/valarray:1202:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__bitwise_and, std::_Constant, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__bitwise_and, _Tp>::result_type> std::operator&(const typename valarray<_Tp>::value_type&, const valarray<_Tp>&)'
 1202 | _DEFINE_BINARY_OPERATOR(&, __bitwise_and)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1202:1: note:   template argument deduction/substitution failed:
a.cc:83:13: note:   'std::set<int>' is not derived from 'const std::valarray<_Tp>'
   83 |   if((st1 & st2).size()>=1) flag=true;
      |             ^~~
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:41:
/usr/include/c++/14/cstddef:141:3: note: candidate: 'constexpr std::byte std::operator&(byte, byte)'
  141 |   operator&(byte __l, byte __r) noexcept
      |   ^~~~~~~~
/usr/include/c++/14/cstddef:141:18: note:   no known conversion for argument 1 from 'std::set<int>' to 'std::byte'
  141 |   operator&(byte __l, byte __r) noexcept
      |             ~~~~~^~~
In file included from /usr/include/c++/14/streambuf:43,
                 from /usr/include/c++/14/bits/streambuf_iterator.h:35,
                 from /usr/include/c++/14/iterator:66,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:54:
/usr/include/c++/14/bits/ios_base.h:84:3: note: candidate: 'constexpr std::_Ios_Fmtflags std::operator&(_Ios_Fmtflags, _Ios_Fmtflags)'
   84 |   operator&(_Ios_Fmtflags __a, _Ios_Fmtflags __b) _GLIBCXX_NOTHROW
      |   ^~~~~~~~
/usr/include/c++/14/bits/ios_base.h:84:27: note:   no known conversion for argument 1 from 'std::set<int>' to 'std::_Ios_Fmtflags'
   84 |   operator&(_Ios_Fmtflags __a, _Ios_Fmtflags __b) _GLIBCXX_NOTHROW
      |             ~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/ios_base.h:134:3: note: candidate: 'constexpr std::_Ios_Openmode std::operator&(_Ios_Openmode, _Ios_Openmode)'
  134 |   operator&(_Ios_Openmode __a, _Ios_Openmode __b) _GLIBCXX_NOTHROW
      |   ^~~~~~~~
/usr/include/c++/14/bits/ios_base.h:134:27: note:   no known conversion for argument 1 from 'std::set<int>' to 'std::_Ios_Openmode'
  134 |   operator&(_Ios_Openmode __a, _Ios_Openmode __b) _GLIBCXX_NOTHROW
      |             ~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/ios_base.h:181:3: note: candidate: 'constexpr std::_Ios_Iostate std::operator&(_Ios_Iostate, _Ios_Iostate)'
  181 |   operator&(_Ios_Iostate __a, _Ios_Iostate __b) _GLIBCXX_NOTHROW
      |   ^~~~~~~~
/usr/include/c++/14/bits/ios_base.h:181:26: note:   no known conversion for argument 1 from 'std::set<int>' to 'std::_Ios_Iostate'
  181 |   operator&(_Ios_Iostate __a, _Ios_Iostate __b) _GLIBCXX_NOTHROW
      |             ~~~~~~~~~~~~~^~~
In file included from /usr/include/c++/14/bits/shared_ptr_atomic.h:33,
                 from /usr/include/c++/14/memory:81,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:56:
/usr/include/c++/14/bits/atomic_base.h:109:3: note: candidate: 'constexpr std::memory_order std::operator&(memory_order, __memory_order_modifier)'
  109 |   operator&(memory_order __m, __memory_order_modifier __mod) noexcept
      |   ^~~~~~~~
/usr/include/c++/14/bits/atomic_base.h:109:26: note:   no known conversion for argument 1 from 'std::set<int>' to 'std::memory_order'
  109 |   operator&(memory_order __m, __memory_order_modifier __mod) noexcept
      |             ~~~~~~~~~~~~~^~~
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:176:
/usr/include/c++/14/future:156:20: note: candidate: 'constexpr std::launch std::operator&(launch, launch)'
  156 |   constexpr launch operator&(launch __x, launch __y) noexcept
      |                    ^~~~~~~~
/usr/include/c++/14/future:156:37: note:   no known conversion for argument 1 from 'std::set<int>' to 'std::launch'
  156 |   constexpr launch operator&(launch __x, launch __y) noexcept
      |                              ~~~~~~~^~~
In file included