#include<iostream>
#include<cmath>
using namespace std;
int n,all,ans=0;
int a[15];
int lowbit(int x){
	return x&(-x);
}
void dfs(int d,int col,int l,int r){
	if(d==n){
		ans++;
		if(ans<=3){
			for(int i=1;i<=n;i++){
				cout<<a[i]<<" ";
			}
			cout<<endl;
		}
		return ;
	}
	int vis=all&(~(col|l|r));
	for(int i=vis;i;i-=lowbit(i)){
		
		int x=lowbit(i);
		a[d+1]=log2(x)+1;
		dfs(d+1,col+x,(l+x)>>1,(r+x)<<1);
	}

} 
int main()
{
  cin>>n;
  all=(1<<n)-1;
  dfs(0,0,0,0);
  cout<<ans;
  
  
  
    

}

这句话什么意思 dfs(d+1,col+x,(l+x)>>1,(r+x)<<1);

求助