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i need to apply modulus e=10^9+7 on the given expression i*(n+k-2)-((i*(i+1)*(n-1))/2) where i is in terms of n and k . n and k are inputted by the user. 2≤N≤10^18 1≤K≤10^18

i tried using modular arithmetic using the basics i.e (a-b)%e=((a%e)-(b%e))%e and (ab)%e=((a%e)(b%e))%e.

//i have taken unsigned long long int as the data type for all variables    
    a=1;
    b=1;
    cin>>n>>k;
    i=(n+k-2)/(n-1);
    //s=(i*(n+k-2))-((i*(n-1)*(i+1))/2
    j=(i+1);
    p=n+k-2;
    q=n-1;
    r=i/2;
    u=j/2;
    if(i%2==0)
    {
        a=(a*i)%e;
        a=(a*p)%e;
        b=(b*r)%e;
        b=(b*q)%e;
        b=(b*j)%e;
        s=a-b;

    }
      else
    {
        a=(a*i)%e;
        a=(a*p)%e;
        b=(b*u)%e;
        b=(b*q)%e;
        b=(b*i)%e;
        s=a-b;

    }
    cout<<s%e<<endl;

i am getting correct answers for small test cases but for large test cases i am not getting the correct answer.

Evg
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Abhay Patro
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  • but i made two different cases for i i.e either its even or either its odd. and since j=i+1 the opposite applies here also. – Abhay Patro Jun 12 '19 at 07:26
  • Please give input values for which you program doesn't work and the expected (correct) answer. – Evg Jun 12 '19 at 07:28

0 Answers0