Language: C++

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

int main(){
  int n;
  cin>>n;
  int A[n+1];
  for(int i=1;i<=n;i++)cin >> A[i];
  map<int,set<int>> m;
  for(int i=1;i<=n;i++) m[A[i]+i].insert(i);
  int ans=0;
  for(int i=1;i<=n;i++){
     if(m.count(i-A[i])){
        auto it=lower_bound(m[i-A[i]].begin(),m[i-A[i]].end(),i);
        if(it!=m[i-A[i]].begin())it--; ans+=it-m[i-A[i]].begin()+1;
     }
  }
   cout<< ans;
}
        

Compiler output:
a.cc: In function 'int main()':
a.cc:15:47: error: no match for 'operator-' (operand types are 'std::_Rb_tree_const_iterator<int>' and 'std::set<int>::iterator' {aka 'std::_Rb_tree<int, int, std::_Identity<int>, std::less<int>, std::allocator<int> >::const_iterator'})
   15 |         if(it!=m[i-A[i]].begin())it--; ans+=it-m[i-A[i]].begin()+1;
      |                                             ~~^~~~~~~~~~~~~~~~~~
      |                                             |                 |
      |                                             |                 _Rb_tree_const_iterator<[...]>
      |                                             _Rb_tree_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:618:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__y.base() - __x.base())) std::operator-(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  618 |     operator-(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:618:5: note:   template argument deduction/substitution failed:
a.cc:15:64: note:   'std::_Rb_tree_const_iterator<int>' is not derived from 'const std::reverse_iterator<_Iterator>'
   15 |         if(it!=m[i-A[i]].begin())it--; ans+=it-m[i-A[i]].begin()+1;
      |                                                                ^
/usr/include/c++/14/bits/stl_iterator.h:1790:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__x.base() - __y.base())) std::operator-(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1790 |     operator-(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1790:5: note:   template argument deduction/substitution failed:
a.cc:15:64: note:   'std::_Rb_tree_const_iterator<int>' is not derived from 'const std::move_iterator<_IteratorL>'
   15 |         if(it!=m[i-A[i]].begin())it--; ans+=it-m[i-A[i]].begin()+1;
      |                                                                ^
In file included from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127:
/usr/include/c++/14/complex:370:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator-(const complex<_Tp>&, const complex<_Tp>&)'
  370 |     operator-(const complex<_Tp>& __x, const complex<_Tp>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:370:5: note:   template argument deduction/substitution failed:
a.cc:15:64: note:   'std::_Rb_tree_const_iterator<int>' is not derived from 'const std::complex<_Tp>'
   15 |         if(it!=m[i-A[i]].begin())it--; ans+=it-m[i-A[i]].begin()+1;
      |                                                                ^
/usr/include/c++/14/complex:379:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator-(const complex<_Tp>&, const _Tp&)'
  379 |     operator-(const complex<_Tp>& __x, const _Tp& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:379:5: note:   template argument deduction/substitution failed:
a.cc:15:64: note:   'std::_Rb_tree_const_iterator<int>' is not derived from 'const std::complex<_Tp>'
   15 |         if(it!=m[i-A[i]].begin())it--; ans+=it-m[i-A[i]].begin()+1;
      |                                                                ^
/usr/include/c++/14/complex:388:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator-(const _Tp&, const complex<_Tp>&)'
  388 |     operator-(const _Tp& __x, const complex<_Tp>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:388:5: note:   template argument deduction/substitution failed:
a.cc:15:64: note:   'std::set<int>::iterator' {aka 'std::_Rb_tree<int, int, std::_Identity<int>, std::less<int>, std::allocator<int> >::const_iterator'} is not derived from 'const std::complex<_Tp>'
   15 |         if(it!=m[i-A[i]].begin())it--; ans+=it-m[i-A[i]].begin()+1;
      |                                                                ^
/usr/include/c++/14/complex:465:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator-(const complex<_Tp>&)'
  465 |     operator-(const complex<_Tp>& __x)
      |     ^~~~~~~~
/usr/include/c++/14/complex:465:5: note:   candidate expects 1 argument, 2 provided
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:406:5: note: candidate: 'template<class _Dom1, class _Dom2> std::_Expr<std::__detail::_BinClos<std::__minus, std::_Expr, std::_Expr, _Dom1, _Dom2>, typename std::__fun<std::__minus, typename _Dom1::value_type>::result_type> std::operator-(const _Expr<_Dom1, typename _Dom1::value_type>&, const _Expr<_Dom2, typename _Dom2::value_type>&)'
  406 |     _DEFINE_EXPR_BINARY_OPERATOR(-, struct std::__minus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:406:5: note:   template argument deduction/substitution failed:
a.cc:15:64: note:   'std::_Rb_tree_const_iterator<int>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   15 |         if(it!=m[i-A[i]].begin())it--; ans+=it-m[i-A[i]].begin()+1;
      |                                                                ^
/usr/include/c++/14/bits/valarray_after.h:406:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__minus, std::_Expr, std::_Constant, _Dom, typename _Dom::value_type>, typename std::__fun<std::__minus, typename _Dom1::value_type>::result_type> std::operator-(const _Expr<_Dom1, typename _Dom1::value_type>&, const typename _Dom::value_type&)'
  406 |     _DEFINE_EXPR_BINARY_OPERATOR(-, struct std::__minus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:406:5: note:   template argument deduction/substitution failed:
a.cc:15:64: note:   'std::_Rb_tree_const_iterator<int>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   15 |         if(it!=m[i-A[i]].begin())it--; ans+=it-m[i-A[i]].begin()+1;
      |                                                                ^
/usr/include/c++/14/bits/valarray_after.h:406:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__minus, std::_Constant, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__minus, typename _Dom1::value_type>::result_type> std::operator-(const typename _Dom::value_type&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  406 |     _DEFINE_EXPR_BINARY_OPERATOR(-, struct std::__minus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:406:5: note:   template argument deduction/substitution failed:
a.cc:15:64: note:   'std::set<int>::iterator' {aka 'std::_Rb_tree<int, int, std::_Identity<int>, std::less<int>, std::allocator<int> >::const_iterator'} is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   15 |         if(it!=m[i-A[i]].begin())it--; ans+=it-m[i-A[i]].begin()+1;
      |                                                                ^
/usr/include/c++/14/bits/valarray_after.h:406:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__minus, std::_Expr, std::_ValArray, _Dom, typename _Dom::value_type>, typename std::__fun<std::__minus, typename _Dom1::value_type>::result_type> std::operator-(const _Expr<_Dom1, typename _Dom1::value_type>&, const valarray<typename _Dom::value_type>&)'
  406 |     _DEFINE_EXPR_BINARY_OPERATOR(-, struct std::__minus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:406:5: note:   template argument deduction/substitution failed:
a.cc:15:64: note:   'std::_Rb_tree_const_iterator<int>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   15 |         if(it!=m[i-A[i]].begin())it--; ans+=it-m[i-A[i]].begin()+1;
      |                                                                ^
/usr/include/c++/14/bits/valarray_after.h:406:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__minus, std::_ValArray, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__minus, typename _Dom1::value_type>::result_type> std::operator-(const valarray<typename _Dom::value_type>&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  406 |     _DEFINE_EXPR_BINARY_OPERATOR(-, struct std::__minus)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:406:5: note:   template argument deduction/substitution failed:
a.cc:15:64: note:   'std::set<int>::iterator' {aka 'std::_Rb_tree<int, int, std::_Identity<int>, std::less<int>, std::allocator<int> >::const_iterator'} is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   15 |         if(it!=m[i-A[i]].begin())it--; ans+=it-m[i-A[i]].begin()+1;
      |                                                                ^
/usr/include/c++/14/valarray:1197:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__minus, std::_ValArray, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__minus, _Tp>::result_type> std::operator-(const valarray<_Tp>&, const valarray<_Tp>&)'
 1197 | _DEFINE_BINARY_OPERATOR(-, __minus)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1197:1: note:   template argument deduction/substitution failed:
a.cc:15:64: note:   'std::_Rb_tree_const_iterator<int>' is not derived from 'const std::valarray<_Tp>'
   15 |         if(it!=m[i-A[i]].begin())it--; ans+=it-m[i-A[i]].begin()+1;
      |                                                                ^
/usr/include/c++/14/valarray:1197:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__minus, std::_ValArray, std::_Constant, _Tp, _Tp>, typename std::__fun<std::__minus, _Tp>::result_type> std::operator-(const valarray<_Tp>&, const typename valarray<_Tp>::value_type&)'
 1197 | _DEFINE_BINARY_OPERATOR(-,