Language: C++

#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#define REP(i,n) for(int i=0;i<n;i++)
#define REPP(i,n) for(int i=1;i<=n;i++)
#define ALL(obj) (obj).begin(), (obj).end()
const double PI = acos(-1);
const double EPS = 1e-15;
long long INF=(long long)1E17;
#define i_7 (long long)(1E9+7)
long mod(long a){
    long long c=a%i_7;
    if(c>=0)return c;
    return c+i_7;
}
using namespace std;
bool prime_(int n){
  if(n==1){
    return false;
  }else if(n==2){
    return true;
  }else{
    for(int i=2;i<=sqrt(n);i++){
      if(n%i==0){
        return false;
      }
    }
    return true;
  }
}

long long gcd_(long long a, long long b){
  if(a<b){
    swap(a,b);
  }
  if(a%b==0){
    return b;
  }else{
    return gcd_(b,a%b);
  }
}
 
long long lcm_(long long x, long long y){
  return (x/gcd_(x,y))*y;
}

int main(){
  
  long long n;
  cin>>n;
  long long p[n];//pの要素は相異なる
  long long place[n+1];
  for(long long i=0;i<n;i++){
    cin>>p[i];
    place[p[i]] = i;
  }
  //vector<long long> left(n,-1);
  //vector<long long> right(n,n) ;
  
  set<long long> s;
  s.insert(-1);
  s.insert(n);
  long long ans = 0;
  long long l,r;
  long long ll,rr;
  for(long long i=n;i>=1;i--){//二番目に大きな値としてiをとる区間の数を調べる
    auto itr_r = s.lower_bound(place[i]);
    r = *itr_r;
    auto itr_l = itr_r - 1;
    l = *itr_l;
    //left[place[i]] = l;
    //right[place[i]] = r;
    if(r!=n && l!=-1){
      rr = *(itr_r + 1);
      ans += i*(place[i]-l)*(rr-r);
      ll = *(itr_l - 1);
      ans += i*(l-ll)*(r-place[i]);
    }else if(r != n){
      rr = *(itr_r + 1);
      ans += i*(place[i]-l)*(rr-r);
    }else if(l != -1){
      ll = *(itr_l - 1);
      ans += i*(l-ll)*(r-place[i]);
    }else{
      ;
    }
    s.insert(place[i]);
  }
  cout<<ans<<endl;
  return 0;
}



Compiler output:
a.cc: In function 'int main()':
a.cc:68:24: error: no match for 'operator-' (operand types are 'std::_Rb_tree_const_iterator<long long int>' and 'int')
   68 |     auto itr_l = itr_r - 1;
      |                  ~~~~~ ^ ~
      |                  |       |
      |                  |       int
      |                  std::_Rb_tree_const_iterator<long long int>
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:68:26: note:   'std::_Rb_tree_const_iterator<long long int>' is not derived from 'const std::reverse_iterator<_Iterator>'
   68 |     auto itr_l = itr_r - 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:68:26: note:   'std::_Rb_tree_const_iterator<long long int>' is not derived from 'const std::move_iterator<_IteratorL>'
   68 |     auto itr_l = itr_r - 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:68:26: note:   'std::_Rb_tree_const_iterator<long long int>' is not derived from 'const std::complex<_Tp>'
   68 |     auto itr_l = itr_r - 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:68:26: note:   'std::_Rb_tree_const_iterator<long long int>' is not derived from 'const std::complex<_Tp>'
   68 |     auto itr_l = itr_r - 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:68:26: note:   mismatched types 'const std::complex<_Tp>' and 'int'
   68 |     auto itr_l = itr_r - 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:68:26: note:   'std::_Rb_tree_const_iterator<long long int>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   68 |     auto itr_l = itr_r - 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:68:26: note:   'std::_Rb_tree_const_iterator<long long int>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   68 |     auto itr_l = itr_r - 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:68:26: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'int'
   68 |     auto itr_l = itr_r - 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:68:26: note:   'std::_Rb_tree_const_iterator<long long int>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   68 |     auto itr_l = itr_r - 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:68:26: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and 'int'
   68 |     auto itr_l = itr_r - 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:68:26: note:   'std::_Rb_tree_const_iterator<long long int>' is not derived from 'const std::valarray<_Tp>'
   68 |     auto itr_l = itr_r - 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(-, __minus)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1197:1: note:   template argument deduction/substitution failed:
a.cc:68:26: note:   'std::_Rb_tree_const_iterator<long long int>' is not derived from 'const std::valarray<_Tp>'
   68 |     auto itr_l = itr_r - 1;
      |                          ^
/usr/include/c++/14/valarray:1197:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__minus, std::_Constant, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__minus, _Tp>::result_type> std::operator-(const typename valarray<_Tp>::value_type&, const valarray<_Tp>&)'
 1197 | _DEFINE_BINARY_OPERATOR(-, __minus)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1197:1: note:   template argument deduction/substitution failed:
a.cc:68:26: note:   mismatched types 'const std::valarray<_Tp>' and 'int'
   68 |     auto itr_l = itr_r - 1;
      |                          ^
a.cc:73:20: error: no match for 'operator+' (operand types are 'std::_Rb_tree_const_iterator<long long int>' and 'int')
   73 |       rr = *(itr_r + 1);
      |              ~~~~~ ^ ~
      |              |       |
      |              |       int
      |              std::_Rb_tree_const_iterator<long long int>
/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_