SPOJ Problem 3442:The last digit

#include<cstdio>
#include<cstring>
int t,x,y,s;
int a[20];
int main(){
    scanf("%d",&t);
    while(t--){
        scanf("%d%d",&x,&y);
        s=2;x%=10;
        a[0]=1;a[1]=x;a[2]=x*x%10;
        while(a[s]!=x)a[++s]=a[s-1]*x%10;
        if (y==0)printf("1\n");else{
            y=(y-1)%(s-1)+1;
            printf("%d\n",a[y]);
        }
    }
}