Noip模拟88 2021.11.2

#include
#define int long long
using namespace std;
const int NN=1e4+5,mod=1e9+7;
namespace AE86{
	auto read=[](){
		int x=0,f=1;char ch=getchar();
		while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
		while(ch>='0'&&ch<='9'){x=(x<<1)+(x<<3)+(ch^48);ch=getchar();}
		return x*f;
	};
	auto write=[](int x,char opt='\n'){
		char ch[20];short len=0;if(x<0)x=~x+1,putchar('-');
		do{ch[len++]=x%10+(1<<5)+(1<<4);x/=10;}while(x);
		for(short i=len-1;i>=0;--i){putchar(ch[i]);}putchar(opt);
	};
}using namespace AE86;
int n,k,m,dp[21][NN],ans;
namespace Math{
	int h[NN],v[NN];
	auto qmo=[](int a,int b,int ans=1){
		int c=mod;for(;b;b>>=1,a=a*a%c)if(b&1)ans=ans*a%c;
		return ans;
	};
	auto prework=[](){
		h[0]=h[1]=1; v[0]=v[1]=1;
		for(int i=2;i=2;i--)v[i]=v[i+1]*(i+1)%mod;
	};
	auto C=[](int n,int m){return (nnum) continue;
		(dp[pos][num]+=dfs(pos-1,num-tmp)*C(k,i)%mod)%=mod;
	}
	return dp[pos][num];
}
namespace WSN{
	inline short main(){
		FILE *wsn=freopen("chess.in","r",stdin);
		wsn=freopen("chess.out","w",stdout);
		n=read();k=read()/2;m=read();prework();
		ans=C(n,k*2);memset(dp,-1,sizeof(dp));
		for(int i=n-2*k;~i;i--)
			ans=(ans-dfs(20,i)*C(n-i-k,k)%mod+mod)%mod;
		write(ans);
		return 0;
	}
}
signed main(){return WSN::main();}