Language: C++

#include<bits/stdc++.h> 
//#include<atcoder/all>
#define rep(i,n) for(int i = 0; i < n; i++)
#define pb push_back
using namespace std;
//using namespace atcoder;
typedef long long ll;

int main(){
    int n;
    cin >> n;
    vector<ll> a(n + 1);
    rep(i, n) cin >> a[i + 1];
    map<ll, int> m;
    rep(i, n) a[i + 1] += a[i];
    rep(i, n + 1)
        m[a[i]]++;
    ll ans = 0;
    rep(i, m.size()){
        auto itr = m.begin() + i;
        ans += *itr * (*itr - 1) / 2;
    }
    cout << ans << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:20:30: error: no match for 'operator+' (operand types are 'std::map<long long int, int>::iterator' {aka 'std::_Rb_tree<long long int, std::pair<const long long int, int>, std::_Select1st<std::pair<const long long int, int> >, std::less<long long int>, std::allocator<std::pair<const long long int, int> > >::iterator'} and 'int')
   20 |         auto itr = m.begin() + i;
      |                    ~~~~~~~~~ ^ ~
      |                           |    |
      |                           |    int
      |                           std::map<long long int, int>::iterator {aka std::_Rb_tree<long long int, std::pair<const long long int, int>, std::_Select1st<std::pair<const long long int, int> >, std::less<long long int>, std::allocator<std::pair<const long long int, int> > >::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:20:32: note:   mismatched types 'const std::reverse_iterator<_Iterator>' and 'int'
   20 |         auto itr = m.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:20:32: note:   mismatched types 'const std::move_iterator<_IteratorL>' and 'int'
   20 |         auto itr = m.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:20:32: note:   'std::map<long long int, int>::iterator' {aka 'std::_Rb_tree<long long int, std::pair<const long long int, int>, std::_Select1st<std::pair<const long long int, int> >, std::less<long long int>, std::allocator<std::pair<const long long int, int> > >::iterator'} is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   20 |         auto itr = m.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:20:32: note:   mismatched types 'const _CharT*' and 'std::_Rb_tree_iterator<std::pair<const long long int, int> >'
   20 |         auto itr = m.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:20:32: note:   mismatched types 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>' and 'int'
   20 |         auto itr = m.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:20:32: note:   'std::map<long long int, int>::iterator' {aka 'std::_Rb_tree<long long int, std::pair<const long long int, int>, std::_Select1st<std::pair<const long long int, int> >, std::less<long long int>, std::allocator<std::pair<const long long int, int> > >::iterator'} is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   20 |         auto itr = m.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:20:32: note:   'std::map<long long int, int>::iterator' {aka 'std::_Rb_tree<long long int, std::pair<const long long int, int>, std::_Select1st<std::pair<const long long int, int> >, std::less<long long int>, std::allocator<std::pair<const long long int, int> > >::iterator'} is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   20 |         auto itr = m.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:20:32: note:   'std::map<long long int, int>::iterator' {aka 'std::_Rb_tree<long long int, std::pair<const long long int, int>, std::_Select1st<std::pair<const long long int, int> >, std::less<long long int>, std::allocator<std::pair<const long long int, int> > >::iterator'} is not derived from 'std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   20 |         auto itr = m.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:20:32: note:   'std::map<long long int, int>::iterator' {aka 'std::_Rb_tree<long long int, std::pair<const long long int, int>, std::_Select1st<std::pair<const long long int, int> >, std::less<long long int>, std::allocator<std::pair<const long long int, int> > >::iterator'} is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   20 |         auto itr = m.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:20:32: note:   'std::map<long long int, int>::iterator' {aka 'std::_Rb_tree<long long int, std::pair<const long long int, int>, std::_Select1st<std::pair<const long long int, int> >, std::less<long long int>, std::allocator<std::pair<const long long int, int> > >::iterator'} is not derived from 'std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   20 |         auto itr = m.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:20:32: note:   mismatched types 'const _CharT*' and 'std::_Rb_tree_iterator<std::pair<const long long int, int> >'
   20 |         auto itr = m.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