平面最近点对

HDU 1007 求平面最近点对距离的一半

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <cmath>
using namespace std;
const double eps = 1e-7;
const int MAXN = 100010;
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 + 1 == right)
    return dist(p[left],p[right]);
    int mid = (left+right)/2;
    double d1 = Closest_Pair(left,mid);
    double d2 = Closest_Pair(mid+1,right);
    d = min(d1,d2);
    int k = 0;
    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 = 0;i <k;i++)
    {
        for(int j = i+1;j < k && tmpt[j].y - tmpt[i].y < d;j++)
        {
            d = min(d,dist(tmpt[i],tmpt[j]));
        }
    }
    return d;
}
int main()
{
    int n;
    while(~scanf("%d",&n) && n)
    {
        for(int i = 0;i < n;i++)
        scanf("%lf%lf",&p[i].x,&p[i].y);
        sort(p,p+n,cmpxy);
        printf("%.2lf\n",Closest_Pair(0,n-1)/2);
    }
    return 0;
}