卡特兰数

Posted 2021-03-11 sxq-study

卡特兰数：https://oi-wiki.org/math/catalan/

 

 

 1 #include <iostream>
 2 using namespace std;
 3 
 4 const int mod = 1e9+7;
 5 
 6 long long qmi(long long a, long long k, long long p)
 7 {
 8     long long res = 1;
 9     while (k)
10     {
11         if (k & 1) res = res * a % p;
12         a = a * a % p;
13         k >>= 1;
14     }
15     return res;
16 }
17 
18 int main(){
19     long long n;cin >> n;
20     long long res = 1;
21     for(int i = 2*n;i > n;--i) res = res * i % mod;
22     for(int i = 1;i <= n;++i) res = res * qmi(i, mod-2, mod) % mod;
23     res = res * qmi(n+1, mod-2, mod) % mod;
24     cout << res << endl;
25     return 0;
26 }

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