Language: C++

#include <bits/stdc++.h>
//#include <boost/multiprecision/cpp_int.hpp>
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
#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()
#define EPS (1e-9)
#define INF (1e17)
#define PI (acos(-1))
//const double PI = acos(-1);
//const double EPS = 1e-15;
//long long INF=(long long)1E17;
#define i_7 (long long)(1e9+7)
//#define i_7 998'244'353
long mod(long a){
    long long c=a%i_7;
    if(c>=0)return c;
    return c+i_7;
}
long long po(long a, long b){
    if(b==0){
        return 1;
    }
    
    long long z = po(a,b/2);
    z = mod(z*z);
    if(b%2!=0){
        z = mod(a*z);
    }
    return z;
}
 
bool prime_(int n){
  if(n==1){
    return false;
  }else if(n==2){
    return true;
  }else{
    for(int i=2;i<=std::sqrt(n);i++){
      if(n%i==0){
        return false;
      }
    }
    return true;
  }
}
 
long long gcd_(long long a, long long b){
  if(a<b){
    std::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;
}
 
//using namespace std;
//using namespace boost::multiprecision;
//using namespace __gnu_pbds;

int main(){
  using namespace std;
  int n, k;
  cin>>n>>k;
  vector<long long> a(n);
  bool all_minus = true;
  REP(i, n){
    cin>>a[i];
    if(a[i] >= 0) all_minus = false;
  }
  auto cmp = [](long long x, long long y) -> bool{
    return abs(x) >= abs(y);
  }
  sort(ALL(a), cmp);
  long long ans = 1;
  if(k == n){
    REP(i, k){
      ans *= a[i];
      ans = mod(ans);
    }
    cout << ans << endl;
    return 0;
  }
  if(all_minus){
    reverse(ALL(a));
    REP(i, k){
      ans *= a[i];
      ans = mod(ans);
    }
    cout << ans << endl;
    return 0;
  }
  
  queue<long long> s;
  deque<long long> pos;
  deque<long long> neg;
  REP(i, n){
    if(a[i] >= 0){
      pos.push_back(a[i]);
    }else{
      neg.push_back(a[i]);
    }
  }
  while(s.size() < k){
    if(s.size() == k - 1){
      long long p1 = pos.front();
      pos.pop_front();
      s.push(p1);
      break;
    }
    if(neg.size() < 2){
      long long p1 = pos.front();
      pos.pop_front();
      s.push(p1);
    }else if(pos.empty()){
      long long n1 = neg.front();
      neg.pop_front();
      long long n2 = neg.front();
      neg.pop_front();
      s.push(n1);
      s.push(n2);
    }else if(pos.size() < 2){
      long long p1 = pos.front();
      pos.pop_front();
      long long n1 = neg.front();
      neg.pop_front();
      long long n2 = neg.front();
      neg.pop_front();
      if(p1 >= n1 * n2){
        s.push(p1);
        neg.push_front(n2);
        neg.push_front(n1);
      }else{
        s.push(n1);
        s.push(n2);
        pos.push_front(p1);
      }
    }else{
      long long p1 = pos.front();
      pos.pop_front();
      long long p2 = pos.front();
      pos.pop_front();
      long long n1 = neg.front();
      neg.pop_front();
      long long n2 = neg.front();
      neg.pop_front();
      if(p1 * p2 >= n1 * n2){
        s.push(p1);
        s.push(p2);
        neg.push_front(n2);
        neg.push_front(n1);
      }else{
        s.push(n1);
        s.push(n2);
        pos.push_front(p2);
        pos.push_front(p1);
      }
    }
  }
  long long ans = 1;
  for(long long x: s){
    ans *= x;
    ans = mod(ans);
  }
  cout << ans << endl;
  return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:82:3: error: expected ',' or ';' before 'sort'
   82 |   sort(ALL(a), cmp);
      |   ^~~~
a.cc:168:13: error: redeclaration of 'long long int ans'
  168 |   long long ans = 1;
      |             ^~~
a.cc:83:13: note: 'long long int ans' previously declared here
   83 |   long long ans = 1;
      |             ^~~
a.cc:169:20: error: no matching function for call to 'begin(std::queue<long long int>&)'
  169 |   for(long long x: s){
      |                    ^
In file included from /usr/include/c++/14/bits/algorithmfwd.h:39,
                 from /usr/include/c++/14/bits/stl_algo.h:59,
                 from /usr/include/c++/14/algorithm:61,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 from a.cc:1:
/usr/include/c++/14/initializer_list:88:5: note: candidate: 'template<class _Tp> constexpr const _Tp* std::begin(initializer_list<_Tp>)'
   88 |     begin(initializer_list<_Tp> __ils) noexcept
      |     ^~~~~
/usr/include/c++/14/initializer_list:88:5: note:   template argument deduction/substitution failed:
a.cc:169:20: note:   'std::queue<long long int>' is not derived from 'std::initializer_list<_Tp>'
  169 |   for(long long x: s){
      |                    ^
In file included from /usr/include/c++/14/string:53,
                 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/range_access.h:52:5: note: candidate: 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(_Container&)'
   52 |     begin(_Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:52:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/range_access.h: In substitution of 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(_Container&) [with _Container = std::queue<long long int>]':
a.cc:169:20:   required from here
  169 |   for(long long x: s){
      |                    ^
/usr/include/c++/14/bits/range_access.h:52:50: error: 'class std::queue<long long int>' has no member named 'begin'
   52 |     begin(_Container& __cont) -> decltype(__cont.begin())
      |                                           ~~~~~~~^~~~~
/usr/include/c++/14/bits/range_access.h:63:5: note: candidate: 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(const _Container&)'
   63 |     begin(const _Container& __cont) -> decltype(__cont.begin())
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:63:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/range_access.h: In substitution of 'template<class _Container> constexpr decltype (__cont.begin()) std::begin(const _Container&) [with _Container = std::queue<long long int>]':
a.cc:169:20:   required from here
  169 |   for(long long x: s){
      |                    ^
/usr/include/c++/14/bits/range_access.h:63:56: error: 'const class std::queue<long long int>' has no member named 'begin'
   63 |     begin(const _Container& __cont) -> decltype(__cont.begin())
      |                                                 ~~~~~~~^~~~~
/usr/include/c++/14/bits/range_access.h:95:5: note: candidate: 'template<class _Tp, long unsigned int _Nm> constexpr _Tp* std::begin(_Tp (&)[_Nm])'
   95 |     begin(_Tp (&__arr)[_Nm]) noexcept
      |     ^~~~~
/usr/include/c++/14/bits/range_access.h:95:5: note:   template argument deduction/substitution failed:
a.cc:169:20: note:   mismatched types '_Tp [_Nm]' and 'std::queue<long long int>'
  169 |   for(long long x: s){
      |                    ^
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:166:
/usr/include/c++/14/valarray:1227:5: note: candidate: 'template<class _Tp> _Tp* std::begin(valarray<_Tp>&)'
 1227 |     begin(valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/valarray:1227:5: note:   template argument deduction/substitution failed:
a.cc:169:20: note:   'std::queue<long long int>' is not derived from 'std::valarray<_Tp>'
  169 |   for(long long x: s){
      |                    ^
/usr/include/c++/14/valarray:1238:5: note: candidate: 'template<class _Tp> const _Tp* std::begin(const valarray<_Tp>&)'
 1238 |     begin(const valarray<_Tp>& __va) noexcept
      |     ^~~~~
/usr/include/c++/14/valarray:1238:5: note:   template argument deduction/substitution failed:
a.cc:169:20: note:   'std::queue<long long int>' is not derived from 'const std::valarray<_Tp>'
  169 |   for(long long x: s){
      |                    ^
a.cc:169:20: error: no matching function for call to 'end(std::queue<long long int>&)'
/usr/include/c++/14/initializer_list:99:5: note: candidate: 'template<class _Tp> constexpr const _Tp* std::end(initializer_list<_Tp>)'
   99 |     end(initializer_list<_Tp> __ils) noexcept
      |     ^~~
/usr/include/c++/14/initializer_list:99:5: note:   template argument deduction/substitution failed:
a.cc:169:20: note:   'std::queue<long long int>' is not derived from 'std::initializer_list<_Tp>'
  169 |   for(long long x: s){
      |                    ^
/usr/include/c++/14/bits/range_access.h:74:5: note: candidate: 'template<class _Container> constexpr decltype (__cont.end()) std::end(_Container&)'
   74 |     end(_Container& __cont) -> decltype(__cont.end())
      |     ^~~
/usr/include/c++/14/bits/range_access.h:74:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/range_access.h: In substitution of 'template<class _Container> constexpr decltype (__cont.end()) std::end(_Container&) [with _Container = std::queue<long long int>]':
a.cc:169:20:   required from here
  169 |   for(long long x: s){
      |                    ^
/usr/include/c++/14/bits/range_access.h:74:48: error: 'class std::queue<long long int>' has no member named 'end'
   74 |     end(_Container& __cont) -> decltype(__cont.end())
      |                                         ~~~~~~~^~~
/usr/include/c++/14/bits/range_access.h:85:5: note: candidate: 'template<class _Container> constexpr decltype (__cont.end()) std::end(const _Container&)'
   85 |     end(const _Container& __cont) -> decltype(__cont.end())
      |     ^~~
/usr/include/c++/14/bits/range_access.h:85:5: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/range_access.h: In substitution of 'template<class _Container> constexpr decltype (__cont.end()) std::end(const _Container&) [with _Container = std::queue<long long int>]':
a.cc:169:20:   required from here
  169 |   for(long long x: s){
      |                    ^
/usr/include/c++/14/bits/range_access.h:85:54: error: 'const class std::queue<long long int>' has no member named 'end'
   85 |     end(const _Container& __cont) -> decltype(__cont.end())
      |                                               ~~~~~~~^~~
/usr/include/c++/14/bits/range_access.h:106:5: note: candidate: 'template<class _Tp, long unsigned int _Nm> constexpr _Tp* std::end(_Tp (&)[_Nm])'
  106 |     end(_Tp (&__arr)[_Nm]) noexcept
      |     ^~~
/usr/include/c++/14/bits/range_access.h:106:5: note:   template argument deduction/substitution failed:
a.cc:169:20: note:   mismatched types '_Tp [_Nm]' and 'std::queue<long long int>'
  169 |   for(long long x: s){
      |                    ^
/usr/include/c++/14/valarray:1249:5: note: candidate: 'template<class _Tp> _Tp* std::end(valarray<_Tp>&)'
 1249 |     end(valarray<_Tp>& __va) noexcept
      |     ^~~
/usr/include/c++/14/valarray:1249:5: note:   template argument deduction/substitution failed:
a.cc:169:20: note:   'std::queue<long long int>' is not derived from 'std::valarray<_Tp>'
  169 |   for(long long x: s){
      |                    ^
/usr/include/c++/14/valarray:1265:5: note: candidate: 'template<class _Tp> const _Tp* std::end(const valarray<_Tp>&)'
 1265 |     end(const valarray<_Tp>& __va) noexcept
      |     ^~~
/usr/include/c++/14/valarray:1265:5: note:   template argument deduction/substitution failed:
a.cc:169:20: note:   'std::queue<long long int>' is not derived from 'const std::valarray<_Tp>'
  169 |   for(long long x: s){
      |                    ^