求组合数板子

 1 ll f[maxn];
 2 void ff()
 3 {
 4     f[0]=1;
 5     for(int i=1;i<=100005;i++)
 6         f[i]=(i*f[i-1])%mod;
 7 }
 8 ll poww(ll n,ll m)
 9 {
10     ll ans = 1;
11     while(m > 0)
12     {
13         if(m & 1)ans = (ans * n) % mod;
14         m = m >> 1;
15         n = (n * n) % mod;
16     }
17     return ans;
18 }
19 ll cc(ll n,ll m)
20 {
21     ll ans=f[n];
22     ans=(ans*poww(f[m],mod-2))%mod;
23     ans=(ans*poww(f[n-m],mod-2))%mod;
24     return ans;
25 }