Language: C++

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

#define pii  pair<int, int>
#define vi vector<int >
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fi first
#define se second
#define sz(x) (x).size()
#define all(x) (x).begin(), (x).end() //Forward traversal
#define rall(x) (x).rbegin, (x).rend() //reverse traversal

#define ll long long
#define ld long double
#define endl "\n"

const ld EPS = 10e-9;
const int INF = 1e9 + 5;
const long long INFLL = (ll)INF * (ll)INF;
const ll MOD = 1e9 + 7;
const ld PI = 3.14159265358979323846;

template <typename T>
ostream& operator<<(ostream& os, const vector<T>& v)
{
    os << "[";
    for (int i = 0; i < (int)v.size(); ++i) {
        os << v[i];
        if (i != (int)v.size() - 1)
            os << ", ";
    }
    os << "]\n";
    return os;
}

template <typename T>
ostream& operator<<(ostream& os, const set<T>& v)
{
    os << "{";
    for (const auto& it : v) {
        os << it;
        if (it != *v.rbegin())
            os << ", ";
    }
    os << "}\n";
    return os;
}

template <typename T>
ostream& operator<<(ostream& os, const unordered_set<T>& v)
{
    os << "{";
    for (const auto& it : v) {
        os << it;
        if (it != *v.rbegin())
            os << ", ";
    }
    os << "}\n";
    return os;
}

template <typename T, typename S>
ostream& operator<<(ostream& os, const map<T, S>& v)
{
    os << "{";
    for (const auto& it : v) {
        os << it.first << " : "
           << it.second;

        if( it != *v.rbegin())
            os  << ", ";
    }

    os << "}\n";
    return os;
}

template <typename T, typename S>
ostream& operator<<(ostream& os, const unordered_map<T, S>& v)
{
    os << "{";
    for (const auto& it : v) {
        os << it.first << " : "
           << it.second;

        if( it != *v.rbegin())
            os  << ", ";
    }

    os << "}\n";
    return os;
}

template <typename T, typename S>
ostream& operator<<(ostream& os, const pair<T, S>& v)
{
    os << "(";
    os << v.first << ", "
       << v.second << ")";
    os << "\n";
    return os;
}

#define DEBUG

#ifdef DEBUG
#define debug(...) __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1>
void __f(const char* name, Arg1&& arg1){
    cerr << name << " : " << arg1;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args){
    const char* comma = strchr(names + 1, ',');cerr.write(names, comma - names) << " : " << arg1<<" | ";__f(comma+1, args...);
}
#else
#define debug(...)
#endif


// __gcd(x, y)

// idea behind binary search: there is monotonically increasing predicate and range [l, r]. Find
// x in range such that x is smallest value for which predicate holds true.
//            int lo = 1, hi = 1e9;
//            while(lo < hi)
//            {
//                ll mid = (lo+hi) / 2;
//                if(predicate(mid))
//                {
//                    hi = mid;
//                }
//                else
//                {
//                    lo = mid+1;
//                }
//            }
//            assert(lo == hi);

// OR: given monotonically decreasing predicate, find x in range such that x is largest value for
// which predicate holds true.

//int x = 0;
//for(int s = max_step; s >= 1; s /= 2)
//{
//    while(predicate(x+s)) x += s;
//}
// after this, x is the largest value for which predicate is true

// How to calculate mid element:
// floor((l+r) / 2) might overflow, use l + floor((r-l)/2)



//ll l = 0, r = s.size()-1;
//ll ans = -1;
//while(l < r)
//{
//    ll mid = l + (r-l) / 2;
//    if(P(mid)) {
//        r = mid;
//        ans = mid;
//    }
//    else
//    {
//        l = mid + 1;
//    }
//}
//
// AND
//
//ll l = 0, r = s.size()-1;
//ll ans = -1;
//while(l <= r)
//{
//    ll mid = l + (r-l) / 2;
//    if(P(mid)) {
//        r = mid-1;
//        ans = mid;
//    }
//    else
//    {
//        l = mid + 1;
//    }
//}
//
// ARE EQUIVALENT

const ll mod = 1e9+7;
struct mint {
  long long x; // typedef long long ll;
  mint(long long x=0):x((x%mod+mod)%mod){}
  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 { mint res(*this);return res+=a;}
  mint operator-(const mint a) const { mint res(*this);return res-=a;}
  mint operator*(const mint a) const { mint res(*this);return res*=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();}
};
istream& operator>>(istream& is, const mint& a) { return is >> a.x;}
ostream& operator<<(ostream& os, const mint& a) { return os << a.x;}


//ll mod(ll a, ll m) {
//    ll r = a % m;
//    if(r < 0)
//        r += m;

//    return r;
//}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);

    int n, k;
    cin >> n >> k;

    vector<ll> a(n);
    bool neg = true;
    for(int i = 0; i < n; i++) {
        cin >> a[i];
        if(a[i] >= 0)
            neg = false;
    }

    if(k == n) {
//        ll prod = 1;
        mint prod = 1;
        for(int i = 0; i < n; i++) {
//            prod = (prod*a[i])%MOD;
//            prod = mod(prod*a[i], MOD);
            prod *= a[i];
        }
        cout << prod << endl;
//        cout << mod(prod, MOD) << endl;
    }
    else if(k%2!=0 && neg) {
        sort(all(a), greater<ll>());
//        ll prod = 1;
        mint prod = 1;
        for(int i = 0; i < k; i++) {
//            prod = (prod*a[i])%MOD;
//            prod = mod(prod*a[i], MOD);
            prod *= a[i];
        }
        cout << prod << endl;
//        cout << mod(prod, MOD) << endl;
    }
    else {
        sort(all(a), [](const ll a, const ll b) {return abs(a) > abs(b); });
//        ll prod = 1;
        mint prod = 1;
        ll lastNegative = 1, lastPositive = -1;
        for(int i = 0; i < k; i++) {
//            prod = (prod*a[i])%MOD;
//            prod = mod(prod*a[i], MOD);
            prod *= a[i];
            if(a[i] < 0) {
                lastNegative = a[i];
            }
            else if(a[i] > 0) {
                lastPositive = a[i];
            }
        }
        if(prod.x >= 0) {
//            cout << mod(prod, MOD) << endl;
            cout << prod << endl;
        }
        else {
            //remove positive, add negative
            ll nextNegative = 1, nextPositive = -1;
            for(int i = k; i < n; i++) {
                if(a[i] < 0) {
                    nextNegative = a[i];
                    break;
                }
            }

            //remove negative, add non-negative
            for(int i = k; i < n; i++) {
                if(a[i] > 0) {
                    nextPositive = a[i];
                    break;
                }
            }

            if(lastNegative != 1 && nextPositive != -1 &&
                    lastPositive != -1 && nextNegative != 1) {
                if(nextNegative*lastNegative < nextPositive*lastPositive) {
//                    prod /= lastPositive;
//                    prod *= nextNegative;
                    prod /= lastNegative;
                    prod *= nextPositive;
                }
                else {
//                    prod /= lastNegative;
//                    prod *= nextPositive;

                    prod /= lastPositive;
                    prod *= nextNegative;
                }
            }
            else if(lastNegative != 1 && nextPositive != -1) {
                prod /= lastNegative;
                prod *= nextPositive;

            }
            else if(lastPositive != -1 && nextNegative != 1) {
                prod /= lastPositive;
                prod *= nextNegative;

            }
            else {
                if(a[N-1] == 0){

                    prod = 0;

                }else{

                    prod = 1;
                    for(int i = 0; i < k; i++) {
                        ans *= (mint) a[n-1-i];
                    }
                }
            }

            cout << prod << endl;

        }
    }

    return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:325:22: error: 'N' was not declared in this scope
  325 |                 if(a[N-1] == 0){
      |                      ^
a.cc:333:25: error: 'ans' was not declared in this scope; did you mean 'abs'?
  333 |                         ans *= (mint) a[n-1-i];
      |                         ^~~
      |                         abs