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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. #define ll long long
  4. void c(ll n,ll r,ll n_r,ll f,ll v)
  5. {
  6.     if(n==max(n_r,r))
  7.     {
  8.         ll mini = min(r,n_r);
  9.         if(mini<=1)
  10.         {
  11.             cout<<f/v;
  12.             return;
  13.         }
  14.         if (r < n_r)
  15.             c(n, r - 1, n_r, f, v * mini);
  16.         else
  17.             c(n, r, n_r - 1, f, v * mini);
  18.         return;
  19.     }
  20.     c(n-1,r,n_r,f*n,v);
  21. }
  22.  
  23. int main()
  24. {
  25.     ll n,m,f=1,v=1;cin>>n>>m;
  26.     if(n==m||m==0)
  27.     {
  28.         cout<<1;
  29.         return 0;
  30.     }
  31.     if(m>n)
  32.     {
  33.         cout<<0;
  34.         return 0;
  35.     }
  36.     c(n,m,n-m,f,v);
  37.     return 0;
  38. }
Success #stdin #stdout 0s 5348KB
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stdout 
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https://ideone.com/iuTsoY
language:
C++ (gcc 8.3)
created:
50 minutes ago
visibility:
public

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