Cod sursa(job #423206)

Utilizator alexandru92alexandru alexandru92 Data 23 martie 2010 16:50:50
Problema Invers modular Scor 100
Compilator cpp Status done
Runda Arhiva educationala Marime 0.86 kb
/* 
 * File:   main.cpp
 * Author: virtualdemon
 *
 * Created on March 23, 2010, 4:30 PM
 */
#include <cstdio>
#include <cstdlib>


/*
 *
 */
using namespace std;
inline int pow( int A, int phi, int N )
{
    int Aphi=1;
    for( ; phi; phi>>=1 )
    {
        if( phi&1 )
        {
            Aphi=(1LL*Aphi*A)%N;
            --phi;
        }
        A=(1LL*A*A)%N;
    }
    return Aphi;
}
inline int getphi( int N )
{
    int phi=N, i, nr;
    for( i=2; i*i <= N; ++i )
    {
        if( 0 == N%i )
        {
            for( nr=0; 0 == N%i; N/=i, ++nr );
            phi/=i; phi*=(i-1);
        }
    }
    if( N > 1 )
        phi/=N, phi*=(N-1);
    return phi;
}
int main( void )
{
    int A, N;
    fscanf( fopen( "inversmodular.in", "rt" ), "%d%d", &A, &N );
    fprintf( fopen( "inversmodular.out", "wt" ), "%d", pow( A, getphi(N)-1, N ) );
    return EXIT_SUCCESS;
}