### vohrab1896's blog

By vohrab1896, history, 6 months ago, ,

Hi CF community! I have been solving this problem(https://www.codechef.com/JUNE19B/problems/CHFING) from quite a few days. Previously, I didn't know about Frobenius Numbers and then I solved this using it but still getting Wrong Answer. Here is my code

#include<bits/stdc++.h>

using namespace std;

long long fast_pow(long long base, long long n,long long M)
{
if(n==0)
return 1;
if(n==1)
return base;
long long halfn=fast_pow(base,n/2,M);
if(n%2==0)
return ( halfn * halfn ) % M;
else
return ( ( ( halfn * halfn ) % M ) * base ) % M;
}
long long findMMI_fermat(long long n,long long M)
{
return fast_pow(n,M-2,M);
}
int main()
{
int t;
long long n,k;
cin>>t;
while(t--)
{
long long a=1000000007;
cin>>n>>k;

if(k==1)cout<<"0"<<endl;
else
{
long long l=findMMI_fermat(n-1,a);
long long f=(((((((k-2)%a)*l)%a)*(k%a))%a+k)%a-1)%a;
if(f<(k))cout<<(k-1)%a<<endl;
else
{
long long count=0;

long long l1=findMMI_fermat(k,a);
long long f1=((f+1)%a*(l1%a))%a;
long long f2;

f2=(((((f1-1)%a)*(f1)%a)%a)/2)%a;

count=((((f2%a)*((n-1)%a))%a+f1)%a-1)%a;

cout<<(f%a-(count)%a+a)%a<<endl;
}
}
}

return 0;
}



Also, I have a doubt in using Fermat's Theorem. In (a/b)%m, if a is not divisible by b, it is giving a large number than expected. Maybe I am somewhere wrong in my concept. Please help if possible. Thanks.