$LOJ$ $2833$ $「JOISC 2018 Day 1」$ 帐篷

链接

背景

(Japan) (Olympiad) (in) (Informatics) (Spring) (Camp) (2018) (Day1) (T3) ， (LOJ) (2833)

题意

咕咕咕

解法

细节

代码

$View$ $Code$

//省略头文件
using namespace std;
inline int read()
{
	int ret=0,f=1;
	char ch=getchar();
	while(ch>'9'||ch<'0')
	{
		if(ch=='-')
			f=-1;
		ch=getchar();
	}
	while(ch>='0'&&ch<='9')
	{
		ret=(ret<<1)+(ret<<3)+ch-'0';
		ch=getchar();
	}
	return ret*f;
}
const int mod=1e9+7;
int h,w,ans;
long long dp[3005][3005];
int main()
{
    h=read();
	w=read();
	for(int i=0;i<=h;i++)
	{
        for(int j=0;j<=w;j++)
		{
            if(!i||!j) 
                dp[i][j]=1;
            else
			{
                dp[i][j]=dp[i][j-1]+4*i*dp[i-1][j-1];
                if(2<=i)
                    dp[i][j]+=i*(i-1)/2*dp[i-2][j-1];
                if(2<=j)
                    dp[i][j]+=i*(j-1)*dp[i-1][j-2];
                dp[i][j]%=mod;
            }
        }
    }
    ans=((dp[h][w]-1)%mod+mod)%mod;
    printf("%d
",ans);
    return 0;
}