Language: C++

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

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;

vll cumsum(vll& A){
  vll cum;
  int N=A.size();
  cum.push_back(0);
  for (int i=0;i<N;++i){
    cum.push_back(cum[i]+A[i]);
  }
  return cum;
}

//[low, high-1]から探す。
int b_search(vll& cum, int low, int high, ll c){
  int lb=low-1, ub=high;
  while(ub-lb>1){
    int mid=(ub+lb)/2;
    if(cum[mid]>=c){ub=mid;}
    else{lb=mid;}
  }
  return ub;
}

int main(){
  int N;cin>>N;
  vll A;
  for (int i=0;i<N;++i){
    ll a;cin>>a;A.push_back(a);
  }

  vll cum=cumsum(A);

  ll smallest=cum[N];
  //i,i+1の間でまんなかを切る
  for (int i=2i<N-1;++i){
    ll lc=cum[i];
    ll hc=cum[N]-cum[i];
    int lub=b_search(cum, 1, i+1, lc/2);
    int hub=b_search(cum, i+1, N+1, uc/2);
    ll B=cumsum[lub];
    ll C=cumsum[i]-cumsum[lub];
    ll D=cumsum[hub]-cumsum[i];
    ll E=cumsum[N]-cumsum[hub];
    ll M=max(B,C);M=max(M,D);M=max(M,E);
    ll m=min(B,C);m=min(m,D);m=min(m, E);
    smallest=min(smallest, M-m);
    if(lub!=1){
      B=cumsum[lub-1];
      C=cumsum[i]-cumsum[lub-1];
      M=max(B,C);M=max(M,D);M=max(M,E);
      m=min(B,C);m=min(m,D);m=min(m, E);
      smallest=min(smallest, M-m);
    }
    if(hub!=i+1){
      D=cumsum[hub-1]-cumsum[i];
      E=cumsum[N]-cumsum[hub-1];
      M=max(B,C);M=max(M,D);M=max(M,E);
      m=min(B,C);m=min(m,D);m=min(m, E);
      smallest=min(smallest, M-m);
    }
  }

  cout << smallest << endl;
  return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:40:16: error: no match for 'operator<' (operand types are 'std::complex<double>' and 'int')
   40 |   for (int i=2i<N-1;++i){
      |              ~~^~~~
      |              |   |
      |              |   int
      |              std::complex<double>
In file included from /usr/include/c++/14/regex:68,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:181,
                 from a.cc:1:
/usr/include/c++/14/bits/regex.h:1143:5: note: candidate: 'template<class _BiIter> bool std::__cxx11::operator<(const sub_match<_BiIter>&, const sub_match<_BiIter>&)'
 1143 |     operator<(const sub_match<_BiIter>& __lhs, const sub_match<_BiIter>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1143:5: note:   template argument deduction/substitution failed:
a.cc:40:19: note:   'std::complex<double>' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   40 |   for (int i=2i<N-1;++i){
      |                   ^
/usr/include/c++/14/bits/regex.h:1224:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator<(__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&, const sub_match<_BiIter>&)'
 1224 |     operator<(const __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1224:5: note:   template argument deduction/substitution failed:
a.cc:40:19: note:   'std::complex<double>' is not derived from 'std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>'
   40 |   for (int i=2i<N-1;++i){
      |                   ^
/usr/include/c++/14/bits/regex.h:1317:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator<(const sub_match<_BiIter>&, __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&)'
 1317 |     operator<(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1317:5: note:   template argument deduction/substitution failed:
a.cc:40:19: note:   'std::complex<double>' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   40 |   for (int i=2i<N-1;++i){
      |                   ^
/usr/include/c++/14/bits/regex.h:1391:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const typename std::iterator_traits<_Iter>::value_type*, const sub_match<_BiIter>&)'
 1391 |     operator<(typename iterator_traits<_Bi_iter>::value_type const* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1391:5: note:   template argument deduction/substitution failed:
a.cc:40:19: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
   40 |   for (int i=2i<N-1;++i){
      |                   ^
/usr/include/c++/14/bits/regex.h:1485:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type*)'
 1485 |     operator<(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1485:5: note:   template argument deduction/substitution failed:
a.cc:40:19: note:   'std::complex<double>' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   40 |   for (int i=2i<N-1;++i){
      |                   ^
/usr/include/c++/14/bits/regex.h:1560:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const typename std::iterator_traits<_Iter>::value_type&, const sub_match<_BiIter>&)'
 1560 |     operator<(typename iterator_traits<_Bi_iter>::value_type const& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1560:5: note:   template argument deduction/substitution failed:
a.cc:40:19: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
   40 |   for (int i=2i<N-1;++i){
      |                   ^
/usr/include/c++/14/bits/regex.h:1660:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type&)'
 1660 |     operator<(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1660:5: note:   template argument deduction/substitution failed:
a.cc:40:19: note:   'std::complex<double>' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   40 |   for (int i=2i<N-1;++i){
      |                   ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51:
/usr/include/c++/14/bits/stl_pair.h:1045:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator<(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1045 |     operator<(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1045:5: note:   template argument deduction/substitution failed:
a.cc:40:19: note:   'std::complex<double>' is not derived from 'const std::pair<_T1, _T2>'
   40 |   for (int i=2i<N-1;++i){
      |                   ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:67:
/usr/include/c++/14/bits/stl_iterator.h:448:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  448 |     operator<(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:448:5: note:   template argument deduction/substitution failed:
a.cc:40:19: note:   'std::complex<double>' is not derived from 'const std::reverse_iterator<_Iterator>'
   40 |   for (int i=2i<N-1;++i){
      |                   ^
/usr/include/c++/14/bits/stl_iterator.h:493:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  493 |     operator<(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:493:5: note:   template argument deduction/substitution failed:
a.cc:40:19: note:   'std::complex<double>' is not derived from 'const std::reverse_iterator<_Iterator>'
   40 |   for (int i=2i<N-1;++i){
      |                   ^
/usr/include/c++/14/bits/stl_iterator.h:1694:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1694 |     operator<(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1694:5: note:   template argument deduction/substitution failed:
a.cc:40:19: note:   'std::complex<double>' is not derived from 'const std::move_iterator<_IteratorL>'
   40 |   for (int i=2i<N-1;++i){
      |                   ^
/usr/include/c++/14/bits/stl_iterator.h:1760:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1760 |     operator<(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1760:5: note:   template argument deduction/substitution failed:
a.cc:40:19: note:   'std::complex<double>' is not derived from 'const std::move_iterator<_IteratorL>'
   40 |   for (int i=2i<N-1;++i){
      |                   ^
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 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/string_view:673:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  673 |     operator< (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:673:5: note:   template argument deduction/substitution failed:
a.cc:40:19: note:   'std::complex<double>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   40 |   for (int i=2i<N-1;++i){
      |                   ^
/usr/include/c++/14/string_view:680:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  680 |     operator< (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:680:5: note:   template argument deduction/substitution failed:
a.cc:40:19: note:   'std::complex<double>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   40 |   for (int i=2i<N-1;++i){
      |                   ^
/usr/include/c++/14/string_view:688:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(__type_identity_t<basic_string_view<_CharT, _Traits> >, basic_string_view<_CharT, _Traits>)'
  688 |     operator< (__type_identity_t<basic_string_view<_CharT, _Traits>> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:688:5: note:   template argument deduction/substitution failed:
a.cc:40:19: note:   mismatched types 'std::basic_string_view<_CharT, _Traits>' and 'int'
   40 |   for (int i=2i<N-1;++i){
      |                   ^
/usr/include/c++/14/bits/basic_string.h:3874:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3874 |     operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3874:5: note:   template argument deduction/substitution failed:
a.cc:40:19: note:   'std::complex<double>' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   40 |   for (int i=2i<N-1;++i){
      |                   ^
/usr/include/c++/14/bits/basic_string.h:3888:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*)'
 3888 |     operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |