POJ1061青蛙的约会（扩展欧几里得）

 #include <cstdio>
 #include <cstring>
 #include <algorithm>
 #include <math.h>
 #include <iostream>
 #include <stack>
 #include <set>
 #include <queue>
 #define MAX(a,b) (a) > (b)? (a):(b)
 #define MIN(a,b) (a) < (b)? (a):(b)
 #define mem(a) memset(a,0,sizeof(a))
 #define INF 1000000007
 #define MAXN 20005
 using namespace std;

 __int64 GCD(__int64 a,__int64 b)
 {
     return a%b==?b:GCD(b,a%b);
 }

 void gcd(__int64 a,__int64 b,__int64 &x,__int64 &y)
 {
     if(!b){x=;y=;}
     else{gcd(b,a%b,y,x); y-=x*(a/b);}
 }

 int main()
 {
     __int64 X,Y,M,N,L;
     while(~scanf("%I64d %I64d %I64d %I64d %I64d",&X,&Y,&M,&N,&L))
     {
         __int64 a = (N-M), b = L, c = (X-Y);
         __int64 g = GCD(a,b);
         if(c%g){ printf("Impossible\n"); continue;}
         __int64 x, y;
         gcd(a, b, x, y);
         x*=(c/g);
         if(x>)x%=(b/g);
         else x=x%(b/g)+(b/g);
         printf("%I64d\n",x);
     }
     return ;
 }