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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3. typedef long long ll;
  4.  
  5. const int maxn = 600100;
  6. const int mod = 1e9+7;
  7.  
  8. ll fac[maxn+100],inv[maxn+100],power[maxn+100];
  9.  
  10. int a,b,c;
  11.  
  12. ll comb(int a,int b)
  13. {
  14.     return fac[a]*inv[b]%mod*inv[a-b]%mod;
  15. }
  16. ll comb(int a,int b,int c)
  17. {
  18.     return fac[a+b+c]*inv[a]%mod*inv[b]%mod*inv[c]%mod;
  19. }
  20. int calc(int k)
  21. {
  22.     int d = b - c;
  23.     int res=0;
  24.     for(int t1 = 0;2 * t1 + d <= k;t1++)
  25.     {
  26.         int t2 = t1 + d;
  27.         int t3 = k - t1 - t2;
  28.         if(c - t1 - t3 < 0) continue;
  29.         res = (res + comb(t1,t2,t3) * comb(c - t1 - t3 + k-1,k-1) % mod * power[t3] % mod)%mod;
  30.     }
  31.     return res;
  32. }
  33. ll solve(int a)
  34. {
  35.     return ((2LL*calc(a)%mod + calc(a+1))%mod + calc(a-1))%mod;
  36. }
  37. int main()
  38. {
  39.     fac[0]=1;
  40.     for(int i=1;i<=maxn;i++) {
  41.       fac[i]=fac[i-1]*i%mod;
  42.     }
  43.     inv[1]=1;
  44.     inv[0]=1;
  45.     for(int i=2;i<=maxn;i++) {
  46.       inv[i]=(mod-(mod/i)*inv[mod%i]%mod)%mod;
  47.     }
  48.     for(int i=1;i<=maxn;i++)  {
  49.       inv[i]=inv[i-1]*inv[i]%mod;
  50.     }
  51.     power[0]=1;
  52.     for(int i=1;i<=maxn;i++) {
  53.       power[i]=(power[i-1]*2)%mod;
  54.     }
  55.     while(cin>>a>>b>>c)
  56.     {
  57.         if(a<c) swap(a,c);
  58.         if(a<b) swap(a,b);
  59.         if(b<c) swap(b,c);
  60.         std::cout << solve(a) << '\n';
  61.     }
  62.     return 0;
  63. }
Success #stdin #stdout 0s 30128KB
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https://ideone.com/0gpXJI
language:
C++14 (gcc 8.3)
created:
6 years ago
visibility:
public

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