HackerEarth Power Failure problem solution

In this HackerEarth Power Failure problem solution, Dexter is a young genius. He is so smart that he has built a big laboratory for himself. His rival’s name is Mandark. Dexter’s laboratory has developed a power failure due to a prank played on him by Mandark. He decided to buy batteries to temporarily provide power to his lab. His lab has n machines. The ith machine requires a battery with a voltage rating of at least Vi volts (1 <= I <= n). Dexter went to the local electronics shop. They have one battery of each voltage rating from 1 to M. Dexter is very suspicious of his rival Mandark. He thinks that Mandark has planted bombs in batteries with a prime voltage rating. He doesn’t want those batteries. As his lab computer is not working, Dexter wants you to find out the number of ways he can buy batteries for each of his machines.

HackerEarth Power Failure problem solution.

#include<iostream>
#include<algorithm>
#define MOD 1000000007
using namespace std;
int main()
{
    int primes[100001]={0},i,j;
    i=2;
    primes[0]=1;
    primes[1]=1;
    while(i*i<=100000)
    {
        if(primes[i]==1)
        {
            i++;
            continue;
        }
        j=i*2;
        while(j<=100000)
        {
            primes[j]=1;
            j+=i;
        }
        i++;
    }
    int primeslt[100001]={0};
    i=1;
    while(i<=100000)
    {
        primeslt[i]=primeslt[i-1];
        if(primes[i]==0)
            primeslt[i]++;
        i++;
    }
//    cout<<primeslt[100000];
    int t,n,m;
    cin>>t;
    while(t--)
    {
        cin>>n>>m;
        i=0;
        int volts[100000];
        while(i<n)
        {
            cin>>volts[i];
            i++;
        }
        sort(volts,volts+n);
        i=n-1;
        long long totways=1;
        while(i>=0)
        {
            int thisways=m-volts[i]+1;
            int alreadyused=n-i-1;
            int cannotuse=primeslt[m]-primeslt[volts[i]-1];
            thisways-=(alreadyused+cannotuse);
            if(thisways<=0)
            {
                break;
            }
            totways=(totways*thisways)%MOD;
            i--;
        }
        if(i!=-1)
            cout<<"0"<<endl;
        else
            cout<<totways<<endl;
;
    }
    return 0;
}

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