WA in FIBOSUM

[udit_iiita]

hello everyone,
I solved this problem

https://www.spoj.pl/problems/FIBOSUM/

but i am getting wa.
Here is my code

#include <iostream>
#include <cmath>
#define phi 1.61803398874989484820458683436563811772030917980576286213544862270526046281890244970720720418939113748475408807538689175212663386222353693179318006076672635443338908659593958290563832266131992829026788
using namespace std;
long int sum_fibonacci(long int n){
        return round((pow(phi,n+2)/sqrt(5)));
}
int main(){
        int t,i=0;
    long int n,m,ans=0;
    cin>>t;

    while(i<t)
    {
            cin >> n >> m;
            ans=sum_fibonacci(m) - sum_fibonacci(n-1);
            ans = ans % 1000000007;
            cout<< ans << endl;
            i++;
    }
    return 0;
}

can someone give me some more tricky test cases?????

[michi]

What do you think how your defined "phi" could be represented in a computer?
en.wikipedia.org/wiki/Floating_point
There is no automatic arbitrary float length.

[udit_iiita]

can you please tell me is there any other way to define this phi???
or is there any inbuilt functionality in c++ to use phi

[michi]

You can define it as a string. But then it will be really difficult to calculate with it (i.e. pow...)
I think you need a completely different approach.

BTW: There's no inbuilt, as i know.

[avi_iiita_sof]

One other reason for getting WA may be that the number of digits in the 1000th fibbonacci number is 209 & it increaes further as n increases, So the long int which you have used would not be able to hold such a big value. Also in the question the upper limit for input is 10^9.
http://mathforum.org/library/drmath/view/52700.html

[mukesh_iiitm]

Edit Posted in problem archives section