Mai intai trebuie sa te autentifici.
Cod sursa(job #2576227)
Utilizator | Data | 6 martie 2020 17:57:15 | |
---|---|---|---|
Problema | Invers modular | Scor | 10 |
Compilator | cpp-64 | Status | done |
Runda | Arhiva educationala | Marime | 0.99 kb |
#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("inversmodular.in");
ofstream fout("inversmodular.out");
int n, a;
long long x;
int prim(int n)
{
if(n<2)
return 0;
if(n%2==0 && n>2)
return 0;
for(int d=3;d*d<=n;d+=2)
if(n%d==0)
return 0;
return 1;
}
long long P(int a, int n, int mod)
{
long long p=1;
while(n)
{
if(n%2==1)
p=((p%mod)*(a%mod))%mod;
a=((a%mod)*(a%mod))%mod;
n/=2;
}
return p;
}
int Phi(int n)
{
int r=n, d=2;
while(n>1)
{
if(n%d==0)
{
r=r/d*(d-1);
while(n%d==0)
n/=d;
}
d++;
if(d*d>n)
d=n;
}
return r;
}
int main()
{
fin >> a >> n;
// Inversul moduelar a lui a
if(prim(n))
x=P(a,n-1,n);
else
x = P(a,Phi(n)-1,n);
fout << x%n;
return 0;
}