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## bitset + O2优化 32ms

Posted by ACAccepted at 2019-02-11 19:18:04 on Problem 2436 and last updated at 2019-02-11 19:18:33
```#include <cstdio>
#include <bitset>
#pragma GCC optimize(2)
%:pragma GCC optimize(2)                                    //O2优化，选其一即可。
using namespace std;

int read()
{
int x=0,f=1;char c=getchar();
while (c<'0' || c>'9'){if (c=='-')f=-1;c=getchar();}
while (c>='0'&&c<='9'){x=(x<<3)+(x<<1)+c-48;c=getchar();}
return x*f;
}

const int MAXN=1010;
const int MAXD=20;
int n,d,k,m,ans;
bitset<MAXD> cow[MAXN];
bitset<MAXD> down;

void dfs(int vis,int now,bitset<MAXD> down)
{
if (now+d-vis+1<k)return ;
if (now==k)
{
int res=0;
bitset<MAXD> a;
for (int i=1;i<=n;i++)
{
a=down&cow[i];
if (a==cow[i])res++;
}
if (res>ans)ans=res;
return ;
}
for (int i=vis;i<=d;i++)
{
down[i]=1;
dfs(i+1,now+1,down);
down[i]=0;
}
}

int main()
{
n=read();d=read();k=read();
for (int i=1;i<=n;i++)
{
m=read();
while (m--)cow[i].set(read());
}
ans=0;
dfs(1,0,down);
printf("%d\n",ans);
return 0;
}```

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