[training Day2] sculpture

Sculpture

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Their thinking

Golden Classic pressure $DP$, set up $f_i$ Indicates that the selection status is $i$ Total number of schemes , Enumerate the last selected number $j$ To transfer , The dynamic transfer equation is ：$$f_i=\sum _{j\in i}^n{f}_{i-1<<j}$$\

code

#include<iostream>
#include<cstdio>
#define int long long
using namespace std;

int n,m;
int f[1<<21];
int a[30][30];

int g(int i)
{
    
	int s=0;
	while(i)
		s+=i&1,i>>=1;
	return s;
}

signed main()
{
    
	cin>>n>>m;
	for(int i=1;i<=m;i++)
	{
    
		int x,y;
		scanf("%lld%lld",&x,&y);
		a[x][y]=1;
	}
	f[0]=1;
	for(int i=0;i<(1<<n);i++)
		for(int j=0;j<n;j++)
			if(i&(1<<j)&&!a[g(i)][j+1])
				f[i]+=f[i-(1<<j)];
	cout<<f[(1<<n)-1]<<endl;
}