Language: C++

#include <bits/stdc++.h>
#include <stdlib.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> P;
typedef pair<ll,ll> llP;

ll mod(ll a, ll b){
  ll ret=a%b;
  if(ret<0) ret+=b;
  return ret;
}

ll modpow(ll a,ll b,ll c){
  ll res=1;
  while(b>0){
    if(b&1) res=mod(res*a,c);
    a=mod(a*a,c);
    b>>=1;
  }
  return res;
}

int main() {
  ll MOD=1000000007;
  int n,k;
  cin>>n>>k;
  int a[n];
  int ne=0,po=0,ze=0;
  vector<int> pos,nes,s;
  multiset<int> pom,nem;
  int ne_ma=-1000000001,ne_mi=0,po_ma=0,po_mi=1000000001;
  for(int i=0;i<n;i++){
    cin>>a[i];
    if(a[i]<0) {
      ne++;
      if(a[i]<ne_mi) ne_mi=a[i];
      if(a[i]>ne_ma) ne_ma=a[i];
      nes.push_back(a[i]);
      s.push_back(abs(a[i]));
      nem.insert(a[i]);
    }
    if(a[i]>0) {
      po++;
      if(a[i]<po_mi) po_mi=a[i];
      if(a[i]>po_ma) po_ma=a[i];
      pos.push_back(a[i]);
      s.push_back(a[i]);
      pom.insert(a[i]);
    }
    if(a[i]==0) ze++;
  }
  int in=ne+po;
  sort(s.begin(),s.end());sort(nes.begin(),nes.end());sort(pos.begin(),pos.end());
  ll ans;
  if(n-ze<k or (ze>=1 and po==0) or (n-ze==k and ne%2==1)){
    ans=0;
  }
  else if(n==k){
    ans=1;
    for(int i=0;i<n;i++){
      ans=mod(ans*a[i],MOD);
    }
  }
  else if(n==ne){
    ans=1;
    if(k%2==0){
      for(int i=n-k;i<n;i++){
        ans=mod(ans*s[i],MOD);
      }
    }
    else{
      for(int i=0;i<k;i++){
        ans=mod(ans*s[i],MOD);
      }
      ans=mod(-1*ans,MOD);
    }
  }
  else{
    int cur_p=po-1,cur_n=0;
    ans=1;
    for(int i=0;i<k-1;i++){
      if(cur_p<0){
        cur_n++;
        continue;
      }
      if(s[n-1-i]==pos[cur_p]) cur_p--;
      else cur_n++;
    }
    if((s[n-k]==pos[cur_p] and cur_n%2==0) or (s[n-k]=-1*nes[cur_n]) and cur_n%2==1){
      for(int i=0;i<k;i++){
        ans=mod(ans*s[n-1-i],MOD);
      }
    }
    else if(cur_n%2==1 and (cur_n==ne or cur_p=0)){
      bool temp=true;
      for(int i=0;i<k-1;i++){
        if(s[n-1-i]==-1*nes[cur_n-1] and temp){
          temp=false;
          continue;
        }
        ans=mod(ans*s[n-1-i],MOD);
      }
      ans=mod(ans*s[n-k,MOD]);
    }
    else if(cur_n%2==1){
      ll com1=nes[cur_n-1]*nes[cur_n],com2=pos[cur_p]*pos[cur_p-1];
      if(com1>com2){
        for(int i=0;i<k-1;i++){
          ans=mod(ans*s[n-1-i],MOD);
        }
        ans=mod(-1*nes[cur_n]*ans,MOD);
      }
      else{
        bool temp =true;
        for(int i=0;i<k-1;i++){
          if(s[n-1-i]==-1*nes[cur_n-1] and temp){
            temp=false;
            continue;
          }
          ans=mod(ans*s[n-1-i],MOD);
        }
        ans=mod(ans*pos[cur_p],MOD);
        ans=mod(ans*pos[cur_p+1],MOD);
      }
    }
    else if(cur_n%2==0 and (cur_p=-1 or cur_n=ne)){
      bool temp=true;
      for(int i=0;i<k-1;i++){
        if(s[n-1-i]==pos[cur_p+1] and temp){
          temp=false;
          continue;
        }
        ans=mod(ans*s[n-1-i],MOD);
      }
      ans=mod(ans*s[n-k],MOD);
    }
  }
  cout<<ans<<endl;
  return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:95:39: error: lvalue required as left operand of assignment
   95 |     else if(cur_n%2==1 and (cur_n==ne or cur_p=0)){
      |                             ~~~~~~~~~~^~~~~~~~
a.cc:104:14: error: too few arguments to function 'll mod(ll, ll)'
  104 |       ans=mod(ans*s[n-k,MOD]);
      |           ~~~^~~~~~~~~~~~~~~~
a.cc:8:4: note: declared here
    8 | ll mod(ll a, ll b){
      |    ^~~
a.cc:127:38: error: lvalue required as left operand of assignment
  127 |     else if(cur_n%2==0 and (cur_p=-1 or cur_n=ne)){
      |                                   ~~~^~~~~~~~