TopCoder SRM 477 CarelessSecretary
1283 단어 topcoder
코드:
#include<iostream>
#include<cstring>
#include<cstdio>
#include<string>
#include<set>
#include<map>
#include<cmath>
#include<algorithm>
#include<vector>
#include<cmath>
#include<queue>
#include<stack>
//#define ull unsigned long long
#define ll long long
using namespace std;
const int INF=0x3f3f3f3f;
const int MOD=1000000007;
const ll LMOD=1000000007;
const double eps=1e-6;
const int N=1050;
ll f[N];
ll c[N][N];
class CarelessSecretary
{
public:
int howMany(int n,int k)
{
f[1]=0;f[2]=1;
for(int i=3;i<N;++i)
f[i]=((i-1)*(f[i-1]+f[i-2]))%LMOD;
memset(c,0,sizeof(c));
for(int i=0;i<N;++i)
for(int j=0;j<=i;++j)
{
if(i==j||j==0)
c[i][j]=1;
else
c[i][j]=(c[i-1][j]+c[i-1][j-1])%LMOD;
}
ll sum=0;
int w=n-k;
for(int i=0;i<=w;++i)
{
sum=(sum+c[w][i]*f[n-i])%LMOD;
//cout<<c[w][i]<<" "<<f[n-i]<<endl;
//cout<<sum<<endl;
}
return (int)sum;
}
};