Language: C++

#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); ++i)
using namespace std;
using ll = long long;
using P = pair<int,int>;

// auto mod int
// https://youtu.be/L8grWxBlIZ4?t=9858
// https://youtu.be/ERZuLAxZffQ?t=4807 : optimize
// https://youtu.be/8uowVvQ_-Mo?t=1329 : division
const int mod = 1000000007;
//const int mod = 998244353;
struct mint {
  ll x; // typedef long long ll;
  mint(ll x=0):x((x%mod+mod)%mod){}
  mint operator-() const { return mint(-x);}
  mint& operator+=(const mint a) {
    if ((x += a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator-=(const mint a) {
    if ((x += mod-a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator*=(const mint a) { (x *= a.x) %= mod; return *this;}
  mint operator+(const mint a) const { return mint(*this) += a;}
  mint operator-(const mint a) const { return mint(*this) -= a;}
  mint operator*(const mint a) const { return mint(*this) *= a;}
  mint pow(ll t) const {
    if (!t) return 1;
    mint a = pow(t>>1);
    a *= a;
    if (t&1) a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const { return pow(mod-2);}
  mint& operator/=(const mint a) { return *this *= a.inv();}
  mint operator/(const mint a) const { return mint(*this) /= a;}
};
istream& operator>>(istream& is, const mint& a) { return is >> a.x;}
ostream& operator<<(ostream& os, const mint& a) { return os << a.x;}

int main() {
    int n,k;
    cin >> n >> k;

    vector<mint> plus_data;
    vector<mint> minus_data;

    for(int i = 0 ; i < n ; i++){
        int temp;
        cin >> temp;
        if(temp >= 0){
            plus_data.push_back(temp);
        }else{
            minus_data.push_back(-temp);
        }
    }

    sort(plus_data.begin(), plus_data.end());
    reverse(plus_data.begin(), plus_data.end());
    sort(minus_data.begin(), minus_data.end());
    reverse(minus_data.begin(), minus_data.end());
    

    mint ans = 1;

    if(plus_data.size() + minus_data.size() == k){
        //K=Nの時
        for(int i = 0 ; i < plus_data.size() ; i++){
            ans *= plus_data.at(i);
        }
        for(int i = 0 ; i < minus_data.size() ; i++){
            ans *= minus_data.at(i);
        }
    }else{

        if(plus_data.size() < k){
            //正の数がkより少ない場合
            //負の数から正の数へ2つづつ持っていく
            int irekae = (int)(k - plus_data.size());
            irekae = (irekae + 1) / 2;

            if((plus_data.size() % 2) == 1){
                plus_data.pop_back();
            }

            for(int i = 0 ; i < irekae ; i++){
                plus_data.push_back(minus_data.at(2 * i));
                plus_data.push_back(minus_data.at(2 * i + 1));
                minus_data.at(2 * i) = 0;
                minus_data.at(2 * i + 1) = 0;
            }
            sort(plus_data.begin(), plus_data.end());
            reverse(plus_data.begin(), plus_data.end());
            sort(minus_data.begin(), minus_data.end());
            reverse(minus_data.begin(), minus_data.end());

            //負の数の削除
            for(int i = 0 ; i < irekae ; i++){
                minus_data.pop_back();
                minus_data.pop_back();
            }
        }
        if((minus_data.size() % 2) == 1){
            minus_data.pop_back();
        }

        int now_p = plus_data.size() - 2;
        int now_m = 0;
        while(1){
            if(now_p < 0){
                break;
            }
            if(now_m >= minus_data.size()){
                break;
            }

            mint plus_temp = (plus_data.at(now_p)) * (plus_data.at(now_p + 1));
            mint minus_temp = (minus_data.at(now_m)) * (minus_data.at(now_m + 1));
            mint aaa = plus_temp - minus_temp;
            if(aaa < 0){
                plus_data.at(now_p) = minus_data.at(now_m);
                plus_data.at(now_p + 1) = minus_data.at(now_m + 1);
                now_p += 2;
                now_m += 2;
            }else{
                break;
            }
        }

        for(int i = 0 ; i < k ; i++){
            ans *= plus_data.at(i);
        }

    }




    cout << ans << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:124:20: error: no match for 'operator<' (operand types are 'mint' and 'int')
  124 |             if(aaa < 0){
      |                ~~~ ^ ~
      |                |     |
      |                mint  int
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:124:22: note:   'mint' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  124 |             if(aaa < 0){
      |                      ^
/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:124:22: note:   'mint' is not derived from 'std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>'
  124 |             if(aaa < 0){
      |                      ^
/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:124:22: note:   'mint' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  124 |             if(aaa < 0){
      |                      ^
/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:124:22: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
  124 |             if(aaa < 0){
      |                      ^
/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:124:22: note:   'mint' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  124 |             if(aaa < 0){
      |                      ^
/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:124:22: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
  124 |             if(aaa < 0){
      |                      ^
/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:124:22: note:   'mint' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  124 |             if(aaa < 0){
      |                      ^
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:124:22: note:   'mint' is not derived from 'const std::pair<_T1, _T2>'
  124 |             if(aaa < 0){
      |                      ^
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:124:22: note:   'mint' is not derived from 'const std::reverse_iterator<_Iterator>'
  124 |             if(aaa < 0){
      |                      ^
/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:124:22: note:   'mint' is not derived from 'const std::reverse_iterator<_Iterator>'
  124 |             if(aaa < 0){
      |                      ^
/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:124:22: note:   'mint' is not derived from 'const std::move_iterator<_IteratorL>'
  124 |             if(aaa < 0){
      |                      ^
/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:124:22: note:   'mint' is not derived from 'const std::move_iterator<_IteratorL>'
  124 |             if(aaa < 0){
      |                      ^
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:124:22: note:   'mint' is not derived from 'std::basic_string_view<_CharT, _Traits>'
  124 |             if(aaa < 0){
      |                      ^
/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:124:22: note:   'mint' is not derived from 'std::basic_string_view<_CharT, _Traits>'
  124 |             if(aaa < 0){
      |                      ^
/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:124:22: note:   mismatched types 'std::basic_string_view<_CharT, _Traits>' and 'int'
  124 |             if(aaa < 0){
      |                      ^
/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:124:22: note:   'mint' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
  124 |             if(aaa < 0){
      |                      ^
/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,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3888:5: note:   template argument deduction/substitution failed:
a.cc:124:22: note:   'mint' is not derived from 'const std::__cxx11::basic_string<_CharT, _Tr