HDU3920 状压DP+优化+记忆化搜索

先按每个点到射击点的距离排个序，然后记忆化搜索，用状态压缩dp即可

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
using namespace std;

const int MAXN = 21;
#define EPS 1e-8
int n;
struct Point{
		double x,y;
		Point(){}
		Point(double _x,double _y):x(_x),y(_y){}
		void input(){
				scanf("%lf%lf",&x,&y);
		}
}ps[MAXN];
Point o;

double dp[1<<MAXN];
double dis[MAXN][MAXN];
double odis[MAXN];
int MAXS;
inline double pdis(Point a,Point b){
		return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
inline int cmp(Point a,Point b){
		return pdis(o,a) < pdis(o,b);
}

inline double dfs(int u){
		if(dp[u] > EPS)return dp[u];
		if(u == 0)return 0.0;
		int y = 0;
		while (!(u&(1<<y)))y ++;
		int tmp;
		for(int i = y+1; i < n; ++i){
				if(u&(1<<i)){
						tmp = u - (1<<i) - (1<<y);
						double temp = dfs(tmp) + odis[y] + dis[y][i];
						if(dp[u] < -EPS || dp[u] > temp)dp[u] = temp;
				}
		}
		return dp[u] < -EPS ? 0.0 : dp[u];
}

int main(){
		int cas;
		scanf("%d",&cas);
		for(int kcas = 1; kcas <= cas; ++kcas){
				o.input();
				scanf("%d",&n);
				for(int i = 0; i < 2*n; ++i)ps[i].input();
				sort(ps,ps+2*n,cmp);
				n = 2*n;


				for(int i = 0; i < n; ++i)
						for(int j = 0; j < n; ++j){
								dis[i][j] = pdis(ps[i],ps[j]);
						}
				for(int i = 0; i < n; ++i){
						odis[i] = pdis(o,ps[i]);
				}

				MAXS = 1<<n;
				for(int i = 0; i < MAXS; ++i)dp[i] = -1.0;
				dfs(MAXS-1);
				printf("Case #%d: ",kcas);
				printf("%.2lf\n",dp[MAXS-1]);
				

		}
}