POJ 1061青蛙的约会

青蛙的约会

exgcd

#include<cstdio>
#include<iostream>
#define LL long long
using namespace std;

LL x,y,n,m,l;

LL exgcd(LL a,LL b,LL &x,LL &y)
{
    if(b==0) { x=1; y=0; return a;}
    LL r=exgcd(b,a%b,x,y);
    LL t=x; x=y; y=t-a/b*y; 
    return r;
}

int main()
{
    cin>>x>>y>>m>>n>>l;
    LL xx,yy,c,g,a;
    a=m-n; c=y-x; g=exgcd(m-n,l,xx,yy);
    if(c%g!=0)
    {
        printf("Impossible");
        return 0;
    }
    xx=c/g*xx; l/=g;
    if(l<0) l=-l;
    xx=(xx%l+l)%l;
    printf("%lld",xx);
}