代码

#include<bits/stdc++.h>
#pragma GCC optimize("Ofast",3,2)
#define ll long long
using namespace std;
const int P=998244353,N=2009;
int c[N][N],pw[N],f[N][N],g[N][N];
int main(){
	int i,j,k,l,n=600,m=2000;
	f[0][0]=c[0][0]=pw[0]=g[0][0]=1;
	if(n>m)return puts("0"),0;
	for(i=1;i<=m;++i){
		c[i][0]=1,pw[i]=(pw[i-1]<<1)%P;
		for(j=1;j<=i;++j){
			c[i][j]=(c[i-1][j-1]+c[i-1][j])%P;
		}
	}
	for(i=1;i<=n;++i){
		for(j=i,l=m-n+i;j<=l;++j){
			for(k=i-1;k<j;++k)f[i][j]=(f[i][j]+g[i-1][k]*1ll*c[m-k][j-k])%P;
			g[i][j]=f[i][j]*1ll*pw[j]%P;
		}
	}
	for(i=n,j=0;i<=m;++i)j=(j+f[n][i])%P;
	printf("%d",j);
	return 0;
}

评测结果