Acdream a + b

http://acdream.info/problem?pid=1007

两个 long long 相乘会超long long

 #include <cstdio>
 #include <cstring>
 #include <algorithm>
 #define ll long long
 #define maxn 10000
 #define mod 10000000007
 using namespace std;

 ll a[maxn];
 ll n,k,t;
 ll fMul(ll a, ll b) {
     ll t = , y = a;
     while(b) {
         if(b & ) t = (t + y) % mod;
         y = (y + y) % mod;
         b >>= ;
     }
     return t;
 }

 ll modExp(ll a, ll b) {
     ll t = , y = a;
     while(b) {
         if(b & ) t = (fMul(t, y)) % mod;
         y = (fMul(y, y)) % mod;
         b >>= ;
     }
     return t;
 }

 int main()
 {
       scanf("%lld",&t);
       while(t--)
       {
           scanf("%lld%lld",&n,&k);
           ll sum=;
           for(int i=; i<n; i++)
           {
               scanf("%lld",&a[i]);
           }
           for(int i=; i<n; i++)
           {
               a[i]=((a[i]%mod)+mod)%mod;
               ll c=modExp(a[i],k);
               sum=(sum+c)%mod;
           }
           printf("%lld\n",sum);
       }
       return ;
 }