#include <bits/stdc++.h>
using namespace std;
const long long mod=1000000007, half=500000004;
long long dp[3005][3005], fac[3005], invfac[3005], invpow[3005];
long long power(long long a, long long b)
{
if (!b)
return 1;
long long res=power(a, b/2);
if (b&1)
return res*res%mod*a%mod;
else
return res*res%mod;
}
long long nCr(long long n, long long r)
{
return fac[n]*invfac[r]%mod*invfac[n-r]%mod;
}
int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
fac[0]=1;
for (long long i=1; i<=3000; i++)
fac[i]=fac[i-1]*i%mod;
invfac[3000]=power(fac[3000], mod-2);
for (long long i=2999; i>=0; i--)
invfac[i]=invfac[i+1]*(i+1)%mod;
invpow[0]=1;
for (long long i=1; i<=3000; i++)
invpow[i]=invpow[i-1]*half%mod;
for (long long i=0; i<=3000; i++)
dp[0][i]=1;
for (long long i=1; i<=3000; i++)
dp[i][0]=1;
for (long long i=1; i<=3000; i++)
for (long long j=1; j<=3000; j++)
dp[i][j]=(dp[i-1][j-1]*j*4+dp[i-1][j])%mod;
long long n, m, ans=0;
cin >> n >> m;
for (long long i=0; i<=min(n, m/2); i++)
{
for (long long j=0; j<=min((n-i)/2, m-i*2); j++)
{
long long num1=nCr(n, i);
long long num2=fac[m]*invfac[m-i*2]%mod*invpow[i]%mod;
long long num3=nCr(m-i*2, j);
long long num4=fac[n-i]*invfac[n-i-j*2]%mod*invpow[j]%mod;
ans=(ans+num1*num2%mod*num3%mod*num4%mod*dp[n-i-j*2][m-i*2-j])%mod;
}
}
cout << ans-1;
return 0;
}
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
42 ms |
70884 KB |
Output is correct |
| 2 |
Correct |
44 ms |
70960 KB |
Output is correct |
| 3 |
Correct |
52 ms |
70876 KB |
Output is correct |
| 4 |
Correct |
42 ms |
70868 KB |
Output is correct |
| 5 |
Correct |
40 ms |
70876 KB |
Output is correct |
| 6 |
Correct |
43 ms |
70968 KB |
Output is correct |
| 7 |
Correct |
42 ms |
70868 KB |
Output is correct |
| 8 |
Correct |
44 ms |
70932 KB |
Output is correct |
| 9 |
Correct |
57 ms |
70860 KB |
Output is correct |
| 10 |
Correct |
53 ms |
70936 KB |
Output is correct |
| 11 |
Correct |
51 ms |
70856 KB |
Output is correct |
| 12 |
Correct |
40 ms |
70948 KB |
Output is correct |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
42 ms |
70884 KB |
Output is correct |
| 2 |
Correct |
44 ms |
70960 KB |
Output is correct |
| 3 |
Correct |
52 ms |
70876 KB |
Output is correct |
| 4 |
Correct |
42 ms |
70868 KB |
Output is correct |
| 5 |
Correct |
40 ms |
70876 KB |
Output is correct |
| 6 |
Correct |
43 ms |
70968 KB |
Output is correct |
| 7 |
Correct |
42 ms |
70868 KB |
Output is correct |
| 8 |
Correct |
44 ms |
70932 KB |
Output is correct |
| 9 |
Correct |
57 ms |
70860 KB |
Output is correct |
| 10 |
Correct |
53 ms |
70936 KB |
Output is correct |
| 11 |
Correct |
51 ms |
70856 KB |
Output is correct |
| 12 |
Correct |
40 ms |
70948 KB |
Output is correct |
| 13 |
Correct |
43 ms |
70872 KB |
Output is correct |
| 14 |
Correct |
42 ms |
71000 KB |
Output is correct |
| 15 |
Correct |
100 ms |
70968 KB |
Output is correct |
| 16 |
Correct |
47 ms |
70868 KB |
Output is correct |
| 17 |
Correct |
46 ms |
70948 KB |
Output is correct |
| 18 |
Correct |
48 ms |
70968 KB |
Output is correct |
| 19 |
Correct |
84 ms |
70968 KB |
Output is correct |
| 20 |
Correct |
78 ms |
70976 KB |
Output is correct |
| 21 |
Correct |
56 ms |
70952 KB |
Output is correct |
| 22 |
Correct |
64 ms |
70976 KB |
Output is correct |
| 23 |
Correct |
44 ms |
70888 KB |
Output is correct |
| 24 |
Correct |
109 ms |
70972 KB |
Output is correct |
| 25 |
Correct |
93 ms |
70976 KB |
Output is correct |
| 26 |
Correct |
110 ms |
71088 KB |
Output is correct |
| 27 |
Correct |
106 ms |
70968 KB |
Output is correct |
