CF1051D Bicolorings 递推

考试T2，随便推一推就好了~

code:

#include <bits/stdc++.h>
#define N 1015
#define mod 998244353
#define ll long long
#define setIO(s) freopen(s".in","r",stdin) , freopen(s".out","w",stdout)
using namespace std;
ll f[N][N<<1][2][2];
int main()
{
	// setIO("army");
	int i,j,n=2,m,k;
	scanf("%d%d",&m,&k);
	f[1][1][0][0]=1ll;
	f[1][1][1][1]=1ll;
	f[1][2][1][0]=1ll;
	f[1][2][0][1]=1ll;
	for(i=1;i<m;++i)
	{
		for(j=1;j<=k;++j)
		{
			(f[i+1][j][0][0]+=(f[i][j][0][0]+f[i][j][0][1]+f[i][j][1][0])%mod)%=mod;
			(f[i+1][j][1][1]+=(f[i][j][0][1]+f[i][j][1][0]+f[i][j][1][1])%mod)%=mod;
			(f[i+1][j][0][1]+=f[i][j][0][1])%=mod;
			(f[i+1][j][1][0]+=f[i][j][1][0])%=mod;
			(f[i+1][j+1][0][0]+=f[i][j][1][1])%=mod;
			(f[i+1][j+1][1][1]+=f[i][j][0][0])%=mod;
			(f[i+1][j+1][0][1]+=(f[i][j][0][0]+f[i][j][1][1])%mod)%=mod;
			(f[i+1][j+1][1][0]+=(f[i][j][0][0]+f[i][j][1][1])%mod)%=mod;
			(f[i+1][j+2][0][1]+=f[i][j][1][0])%=mod;
			(f[i+1][j+2][1][0]+=f[i][j][0][1])%=mod;
		}
    }
	printf("%lld\n",(f[m][k][0][0]+f[m][k][1][1]+f[m][k][0][1]+f[m][k][1][0])%mod);
	return 0;
}