OJ-Problems-Source/HDOJ/5155_autoAC.cpp
2016-09-10 11:37:56 +08:00

46 lines
1002 B
C++

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#define Mod 1000000007
#define lll __int64
using namespace std;
lll c[55][55];
lll dp[55][55];
void calc()
{
for(int i=0;i<=51;i++)
{
c[i][0] = 1;
for(int j=1;j<=i;j++)
c[i][j] = (c[i-1][j-1]+c[i-1][j])%Mod;
}
}
int main()
{
int n,m,i,j,k,t;
calc();
while(scanf("%d%d",&n,&m)!=EOF)
{
memset(dp,0,sizeof(dp));
dp[0][0] = 1;
for(i=1;i<=n;i++)
{
for(k=1;k<=m;k++)
{
for(j=0;j<=k;j++)
{
for(t=max(1,k-j);t<=k;t++)
{
dp[i][k] = (dp[i][k]+dp[i-1][j]*c[m-j][k-j]%Mod*c[j][t-(k-j)]%Mod)%Mod;
}
}
}
}
printf("%I64d\n",dp[n][m]%Mod);
}
return 0;
}