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 = 0, y = a;
    while(b) {
        if(b & 1) t = (t + y) % mod;
        y = (y + y) % mod;
        b >>= 1;
    }
    return t;
}

ll modExp(ll a, ll b) {
    ll t = 1, y = a;
    while(b) {
        if(b & 1) t = (fMul(t, y)) % mod;
        y = (fMul(y, y)) % mod;
        b >>= 1;
    }
    return t;
}

int main()
{
      scanf("%lld",&t);
      while(t--)
      {
          scanf("%lld%lld",&n,&k);
          ll sum=0;
          for(int i=0; i<n; i++)
          {
              scanf("%lld",&a[i]);
          }
          for(int i=0; i<n; i++)
          {
              a[i]=((a[i]%mod)+mod)%mod;
              ll c=modExp(a[i],k);
              sum=(sum+c)%mod;
          }
          printf("%lld
",sum);
      }
      return 0;
}