洛谷试炼场P1378 油滴扩展(搜索Ex）

题目连接https://www.luogu.org/problemnew/show/P1378

解题思路：利用深度优先搜索，暴力枚举即可，反正最多只有两个点，最大也就搜索6！次

#include<bits/stdc++.h>
using namespace std;
int vis[10],n;
double r[10],x[10],y[10],p;
double xl,yl,x2,y2,s;
const double pi=acos(-1);
double cal(int i)
{
	double s1=min(fabs(x[i]-xl),fabs(x[i]-x2));
	double s2=min(fabs(y[i]-yl),fabs(y[i]-y2));
	double ans=min(s1,s2);
	for(int j=0;j<n;j++)
	{
		if(!vis[j]) continue;
		double d=sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));
		ans=min(ans,max(d-r[j],0.0));
	}
	return ans; 
}
void dfs(int k,double sum)
{
	if(k==n)
	{
		p=max(p,sum);
		return ;
	}
	for(int i=0;i<n;i++)
	{
		if(!vis[i])
		{
			r[i]=cal(i);
			vis[i]=1;
			dfs(k+1,sum+r[i]*r[i]*pi);
			vis[i]=0;
		}
	}
}
int main()
{
	//freopen("t.txt","r",stdin);
	scanf("%d",&n);
	scanf("%lf%lf%lf%lf",&xl,&yl,&x2,&y2);
	//cout<<xl<<" "<<yl<<endl;
	memset(vis,0,sizeof(vis));
	for(int i=0;i<n;i++)
	{
		scanf("%lf%lf",&x[i],&y[i]);
	}
	p=0;
	dfs(0,0);
	s=fabs(xl-x2)*fabs(yl-y2);
	printf("%d",(int)(s-p+0.5));
	return 0;
}