SPOJ Problem 5699:The last digit re-visited

求a^b的最后一位，a有1000位，b是long long。

#include<cstdio>
#include<cstring>
long long y;
char x[1005];
int n,i,s;
int a[10];
int l;
int find(int s,long long r){
    memset(a,0,sizeof(a));
    a[0]=1;
    a[1]=s;a[2]=s*s%10;
    i=2;
    while(a[1]!=a[i])a[++i]=a[i-1]*s%10;
    if (r==0)return 1;
    return a[(r-1)%(i-1)+1];
}
int main(){
    scanf("%d",&n);
    while(n--){
        scanf("%s%lld",&x,&y);
        l=strlen(x);
        printf("%d\n",find(x[l-1]-48,y));
    }
}