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;

}

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