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  1. /**
  2.  * author:  orzvanh14 (  )
  3.  * created: 19.06.2026 19:15:02
  4. **/
  5. #include <bits/stdc++.h>
  6.  
  7. using namespace std;
  8.  
  9. #define int long long
  10. #define nn "\n"
  11.  
  12. const int mod = 1e9 + 7;
  13. const int N = 1e5 + 5;
  14. int D[N];
  15.  
  16. void solve(){
  17.     int n;
  18.     cin >> n;
  19.  
  20.     if (n == 1) {
  21.         cout << 0 << nn;
  22.         return;
  23.     }
  24.     if (n == 2) {
  25.         cout << 1 << nn;
  26.         return;
  27.     }
  28.  
  29.     D[1] = 0;
  30.     D[2] = 1;
  31.     for(int i = 3; i <= n; i++){
  32.         // Công thức: D[n] = (n - 1) * (D[n-1] + D[n-2]) % mod
  33.         D[i] = (i - 1) * (D[i - 1] + D[i - 2]) % mod;
  34.     }
  35.  
  36.     cout << D[n] << nn;
  37. }
  38.  
  39. signed main() {
  40.     ios_base::sync_with_stdio(0);
  41.     cin.tie(0);
  42.     cout.tie(0);
  43.     solve();
  44.     return (0 ^ 0);
  45. }
Success #stdin #stdout 0s 5316KB
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https://ideone.com/rXJmA4
language:
C++14 (gcc 8.3)
created:
10 hours ago
visibility:
public

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