【费马小定理】BZOJ3260-跳

 1 #include<cstdio>
 2 #include<algorithm>
 3 #include<cstring>
 4 #include<map>
 5 #define ll long long
 6 using namespace std;
 7 const int mod=1e9+7;
 8 ll n,m;
 9 
10 ll pow(ll x,ll k)
11 {
12     ll ret=1;
13     for(int i=k;i;i>>=1,x=x*x%mod)
14         if(i&1) ret=ret*x%mod;
15     return ret;
16 }
17 
18 
19 void solve()
20 {
21     scanf("%lld%lld",&n,&m);
22     if(n>m) swap(n,m);
23     m%=mod;
24     ll ans=m+1;
25     
26     ll x=1;
27     for(int i=1;i<=n;i++)
28     {
29         x=(x*(m+i))%mod;
30         x=(x*pow(i,mod-2))%mod;
31         ans=(ans+x)%mod;
32     }
33     printf("%lld\n",ans);
34 
35 }
36 
37 int main()
38 {
39     solve();
40     return 0;
41 }