mirror of
https://github.com/Kiritow/OJ-Problems-Source.git
synced 2024-03-22 13:11:29 +08:00
24 lines
423 B
C++
24 lines
423 B
C++
#include <iostream>
|
|
#include <cstdio>
|
|
#define N 1005
|
|
#define mod 1000000007
|
|
#define ll __int64
|
|
using namespace std;
|
|
ll f[N][N];
|
|
void init()
|
|
{
|
|
int i,j;
|
|
for (i=1;i<N;i++)
|
|
{
|
|
f[i][0]=1;
|
|
for (j=1;j<i;j++) f[i][j]=((j+1)*f[i-1][j]+(i-j)*f[i-1][j-1])%mod;
|
|
}
|
|
}
|
|
int main()
|
|
{
|
|
int n,k;
|
|
init();
|
|
while (scanf("%d%d",&n,&k)!=EOF) cout<<f[n][k]<<endl;
|
|
return 0;
|
|
}
|