poj 1601

扩展欧几里得

#include<iostream>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<cmath>
using namespace std;
long long gcd(long long a,long long b)
{
    if(b==0)
        return a;
    else
    {
        gcd(b,a%b);
    }
}
void extgcd(long long a,long long b,long long &x,long long &y)
{
    if(b==0)
    {
        x=1;
        y=0;
    }
    else
    {
        extgcd(b,a%b,y,x);
        y-=(a/b)*x;

    }
}
long long x,y,m,n,l;
int main()
{
    while(cin>>x>>y>>m>>n>>l)
    {
        if((x-y)%gcd(n-m,l)!=0)
        {

            cout<<"Impossible\n"<<endl;

        }
        else
        {
            long long p,q;
            extgcd((n-m)/gcd(n-m,l),l/gcd(n-m,l),p,q);
            p=p*((x-y)/gcd(n-m,l));
            p=p%l;
            while(p<0)
            {
                p+=l;
            }
            cout<<p<<endl;

        }
    }
    return 0;
}