hdu 1007 N个点中输出2点的最小距离的一半

分治法

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

 # include <iostream>
 # include <cstdio>
 # include <cstring>
 # include <algorithm>
 # include <string>
 # include <cmath>
 # include <queue>
 # include <list>
 # define LL long long
 using namespace std ;

 const double eps = 1e-;
 const int MAXN = ;
 const double INF = 1e20;
 struct Point
 {
    double x,y;
 };

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

 Point p[MAXN];
 Point tmpt[MAXN];
 bool cmpxy(Point a,Point b)
 {
     if(a.x != b.x)return a.x < b.x;
     else return a.y < b.y;
 }
 bool cmpy(Point a,Point b)
 {
     return a.y < b.y;
 }
 double Closest_Pair(int left,int right)
 {
     double d = INF;
     if(left == right)return d;
     if(left +  == right)
     return dist(p[left],p[right]);
     int mid = (left+right)/;
     double d1 = Closest_Pair(left,mid);
     double d2 = Closest_Pair(mid+,right);
     d = min(d1,d2);
     int k = ;
     for(int i = left;i <= right;i++)
     {
         if(fabs(p[mid].x - p[i].x) <= d)
         tmpt[k++] = p[i];
     }
     sort(tmpt,tmpt+k,cmpy);
     for(int i = ;i <k;i++)
     {
         for(int j = i+;j < k && tmpt[j].y - tmpt[i].y < d;j++)
         {
             d = min(d,dist(tmpt[i],tmpt[j]));
         }
     }
     return d;
 }

 int main()
 {
     //freopen("in.txt","r",stdin) ;
     int n;
     while(scanf("%d",&n)== && n)
     {
         for(int i = ;i < n;i++)
         scanf("%lf%lf",&p[i].x,&p[i].y);
         sort(p,p+n,cmpxy);
         printf("%.2lf\n",Closest_Pair(,n-)/);
     }
     return ;
 }