1007：Quoit Design

Problem Description Have you ever played quoit in a playground? Quoit is a game in which flat rings are pitched at some toys, with all the toys encircled awarded. In the field of Cyberground, the position of each toy is fixed, and the ring is carefully designed so it can only encircle one toy at a time. On the other hand, to make the game look more attractive, the ring is designed to have the largest radius. Given a configuration of the field, you are supposed to find the radius of such a ring. Assume that all the toys are points on a plane. A point is encircled by the ring if the distance between the point and the center of the ring is strictly less than the radius of the ring. If two toys are placed at the same point, the radius of the ring is considered to be 0.  

 

Input The input consists of several test cases. For each case, the first line contains an integer N (2 <= N <= 100,000), the total number of toys in the field. Then N lines follow, each contains a pair of (x, y) which are the coordinates of a toy. The input is terminated by N = 0.  

 

Output For each test case, print in one line the radius of the ring required by the Cyberground manager, accurate up to 2 decimal places.  

 

Sample Input 2 0 0 1 1 2 1 1 1 1 3 -1.5 0 0 0 0 1.5 0  

 

Sample Output 0.71 0.00 0.75

 

代码：（转载）

#include <iostream>#include <algorithm>#include <cmath>using namespace std;

struct node{double x,y;}point[100000];int n;

bool cal_less(node p1,node p2){if(p1.x != p2.x) return p1.x < p2.x;else return p1.y < p2.y;}

double dist(node a, node b){return sqrt((a.x - b.x)*(a.x - b.x) + (a.y - b.y)*(a.y - b.y));}

double getmin(double a, double b){ return a<b?a:b;}

double solve(int l,int r){if(l == r)   return 1000000000;if(l == r - 1)   return dist(point[l],point[r]);if(l == r - 2)   return getmin(getmin(dist(point[l],point[l+1]),dist(point[l+1],point[l+2])),dist(point[l],point[l+2]));int i,j,mid = (l+r) >> 1;double curmin = getmin(solve(l,mid),solve(mid+1,r));for(i=l;i<=r;i++)   for(j=i+1;j<=i+5 && j<=r;j++)   {    curmin = getmin(curmin,dist(point[i],point[j]));   }return curmin;}

int main() {int i;while(scanf("%d",&n)!=EOF && n){   for(i=0;i<n;i++)    scanf("%lf %lf",&point[i].x,&point[i].y);   sort(point,point+n,cal_less);   double ans = solve(0,n-1);   printf("%.2lf/n",ans/2);}return 0;}

 

 

原创代码：

 

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

struct point{ double x; double y;}p[1000000];

bool cal_less(point p1,point p2){ if(p1.x != p2.x)   return p1.x < p2.x; else   return p1.y < p2.y;}

double dis(point p1,point p2){ return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));}double getmin(double a,double b){ return a<b?a:b;

}double getmin(point p1,point p2, point p3){ double a=dis(p1,p2); double b=dis(p3,p2); double c=dis(p1,p3); if(a<b) {  if(a<c)   return a;  else   return c; } else  {  if(b>c)   return c;  else   return b; }}double search(int l,int r){ if(l==r)  return 100000000; if(l+1==r)  return dis(p[l],p[r]); if(l+2==r)  return getmin(p[l],p[l+1],p[r]); int mid=(l+r)/2; double curmin=getmin(search(l,mid),search(mid+1,r));

 for(int i=l;i<=mid+1;i++)  if(p[i].x-p[mid].x<=curmin)   for(int j=i+1;j<i+6;j++)    if(dis(p[i],p[j])<curmin)     curmin=dis(p[i],p[j]); return curmin;}

int main(){ int n; scanf("%d",&n); while(n>0) {  for(int i=0;i<n;i++)   scanf("%lf%lf",&p[i].x,&p[i].y);   sort(p,p+n,cal_less);   printf("%.2lf/n",search(0,n-1)/2);  scanf("%d",&n); } return 0;}