最近点对问题 HDU Quoit Design 1007 分治法

#include<cstdio>

#include<cstring>

#include<iostream>

#include<algorithm>

#include<cmath>

#include<stack>

#include<string>

#include<queue>

using namespace std;

const int maxn =  100005;

const long long INF =  0xfffffff;

struct Point

{

    double x, y;

}P[maxn], Temp[maxn];

bool cmp(Point a, Point b)

{

    if(a.x != b.x)

        return  a.x < b.x;

    return a.y < b.y;

}

bool cmpy(Point a, Point b)

{

    return a.y < b.y;

}

double dis(Point a, Point b)

{

    return sqrt( (a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y) );

}

double Colosest(int L,int R)

{

    if(L == R)

        return INF;

    if(L + 1 == R)

        return dis(P[L],P[R]);

    int Mid = (L + R) / 2;

    double d1 = Colosest(L, Mid);

    double d2 = Colosest(Mid + 1, R);


    double  d = min(d1, d2);
//递归找左右两侧的点，最小距离

    int k = 0;



    for(int i = Mid; i >= L; i--)

    {

        if( P[Mid].x - P[i].x < d )

            Temp[k++] = P[i];

        else

            break;

    }



    for(int j = Mid + 1; j <= R; j++)

    {

        if(P[j].x - P[Mid].x < d)

            Temp[k++] = P[j];

        else

            break;

    }

//找出在中间点的可能点对 然后排序

    sort(Temp,Temp+k,cmpy);



    for(int i=0; i<k; i++)

    {
/*需要一个 Temp[j].y - Temp[i].y < d  优化， 不然会超时*/

        for(int j=i+1; j < k && Temp[j].y - Temp[i].y < d ; j++)

        {

            double d3 = dis(Temp[j], Temp[i]);

            if(d3 < d)

                d = d3;

        }

    }

    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,cmp);//先排序

        printf("%.2lf\n", Colosest(0,n-1)/2 );

    }

    return 0;

}