Templates - Chinese remainder theorem to expand GCD +

 1 int exgcd(int a,int b,int &x,int &y)
 2 {
 3     if(b==0)
 4     {
 5         x=1,y=0;
 6         return a;
 7     }
 8     int gcd=exgcd(b,a%b,x,y);
 9     int t=x;
10     x=y;
11     y=t-a/b*y;
12     return gcd;
13 }
14 int China(int W[],int B[],int k)
15 {
16     int x,y,a=0,m,n=1;
17     for(int i=1;i<=k;i++)
18         n*=W[i];
19     for(int i=1;i<=k;i++)
20     {
21         m=n/W[i];
22         exgcd(W[i],m,x,y);
23         a=(a+y*m*B[i])%n;
24     }
25     return a>0?a:(a+n);
26 }

I do not know why, with fast power inversion yuan hung up ...