poj2441 Arrange the Bulls 状压DP

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看了下别人的实现感觉不科学写的那么复杂然而速度是我的1/2= =

我们看到这个很容易联想到棋盘模型n*m,放置n个车,问方案数.

然后愉快地做就行,最简复杂度O(n*2^m),然而窝写成O(m*2^m)其实也无所谓

Problem: 2441User: BPM136Memory: 4812KTime: 235MSLanguage: G++Result: Accepted#include<iostream>#include<cstdio>#include<bitset>#define LL long long#define fo(i,a,b) for(int i=a;i<=b;i++)using namespace std;inline LL read(){LL d=0,f=1;char s=getchar();while(s<'0'||s>'9'){if(s=='-')f=-1;s=getchar();}while(s>='0'&&s<='9'){d=d*10+s-'0';s=getchar();}return d*f;}#define N 25#define M 20unsigned long f[1<<M]={1};bool map[N][N];int n,m;bitset<N>t;int main(){n=read(),m=read();if(n>m){puts("0");return 0;}fo(i,1,n){int k=read();while(k--)map[i][read()]=1;}LL ans=0;fo(i,1,(1<<m)-1){t=i;int num=t.count();if(num>n)continue;fo(k,0,m-1){if((!(i&(1<<k)))||(!(map[num][k+1])))continue;f[i]+=f[i-(1<<k)];}if(num==n)ans+=f[i];}cout<<ans<<endl;return 0;}

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