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  1. #include <bits/stdc++.h>
  2. #define endl "\n"
  3. #define mod 1000000007
  4. #define ll long long int
  5. using namespace std;
  6.  
  7. ll modin(ll a)
  8. {
  9.     ll x = 1LL, y = a, b=(mod-2LL);
  10.     while(b>0)
  11.     {
  12.         if(b&1)
  13.         {
  14.             x=(x*y);
  15.             if (x>=mod) x=x%mod;
  16.         }
  17.         y = (y*y);
  18.         if (y>=mod) y=y%mod;
  19.         b=b>>1; // b/=2
  20.     }
  21.     return x;
  22. }
  23.  
  24. int main()
  25. {
  26.     ios::sync_with_stdio(false);
  27.     ll t;
  28.     cin>>t;
  29.     ll n,x,m,temp1,ans,temp2,temp3,temp4;
  30.     ll a[100006];
  31.     while (t--)
  32.     {
  33.         ans=0;
  34.         temp1=0;
  35.         temp2=0;
  36.         temp3=0;
  37.         temp4=0;
  38.         cin>>n>>x>>m;
  39.         for (ll i=1LL;i<=n;i++)
  40.         {
  41.             cin>>a[i];
  42.             a[i]%=mod;
  43.         }
  44.         if (x==1)
  45.             cout<<(a[1]%mod)<<endl;
  46.         else if (m==1)
  47.         {
  48.             for (ll i=1LL;i<=x;i++)
  49.             {
  50.                 ans = (ans + (a[i]%mod))%mod;
  51.             }
  52.         }
  53.         else
  54.         {
  55.             temp1 = 1LL;
  56.             ans = ((temp1*(a[x]%mod))%mod);
  57.             temp3 = m;
  58.             temp4 = 1LL;
  59.             for (ll i=1LL;i<x;i++)
  60.             {
  61.                 temp2 = (((temp3%mod)*(modin(temp4)%mod))%mod);
  62.                 temp1 = (temp1*temp2)%mod;
  63.                 ans = ((ans+((temp1*(a[x-i]%mod))%mod))%mod);
  64.                 temp3++;
  65.                 temp4++;
  66.             }
  67.             cout<<(ans%mod)<<endl;
  68.         }
  69.     }
  70.     return 0;
  71. }
  72.  
Success #stdin #stdout 0s 4116KB
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https://ideone.com/q8MaoZ
language:
C++ (gcc 8.3)
created:
10 years ago
visibility:
secret

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