poj1061青蛙的约会(扩展欧几里德）

http://poj.org/problem?id=1061

这里解释的很详细。。http://blog.csdn.net/SwordHoly/article/details/4423543

#include <iostream>
#include<cstdio>
#include<string.h>
#include<cmath>
#define LL long long
using namespace std;
LL k,t,d;
LL exgcd(LL a,LL b)
{
    if(b==0)
    {
        k = 1;
        t = 0;
        d = a;
        return a;
    }
    LL egcd = exgcd(b,a%b);
    LL temp = k;
    k = t;
    t = temp-(a/b)*t;
    return egcd;
}
int main()
{
    LL L,a,b,x,y,m,n;
    cin>>x>>y>>m>>n>>L;
    a = m-n;
    b = y-x;
    if(a<0)
    {
        a = -a;
        b = -b;
    }
    exgcd(a,L);
    if(b%d!=0)
    printf("Impossible\n");
    else
    {
         k = k*b/d;
         L = L/d;
         if(k>=0)
         k = k%L;
         else
         k = k%L+L;
         cout<<k<<endl;
    }
    return 0;
}