平面中有若干个点，寻找距离最近的两个点，输出其编号

代码：

#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <map>
#include <stdio.h>
using namespace std;

struct Point
{
    double m_x, m_y;
    Point():m_x(0.0),m_y(0.0) {}
    Point(double x, double y):m_x(x),m_y(y) {}
    bool operator==(const Point& p) const
    {
        return m_x==p.m_x && m_y==p.m_y;
    }
};

ostream& operator<<(ostream& os, const Point& p)
{
    return os << "(" << p.m_x << "," << p.m_y << ")";
}
template<class T, class Pr>
void insert_sort(vector<T> &vec, int l, int r, Pr pred)
{
    int i, j;
    for (i=l+1; i<=r; i++)
    {
        T tmp = vec[i];
        for (j=i-1; j>=l && pred(tmp,vec[j]); j--)
            vec[j+1]=vec[j];
        vec[j+1] = tmp;
    }
}
template<class T>
int get_position(vector<T> &vec, int l, int r, T key)
{
    for (int i=l; i<=r; i++)
        if (key == vec[i])
            return i;
    return -1;
}
template<class T, class Pr>
int partition(vector<T> &vec, int l, int r, Pr pred)
{
    int i, j;
    for (i=l+1,j=l; i<=r; i++)
    {
        if (pred(vec[i],vec[l]))
        {
            ++j;
            swap(vec[i],vec[j]);
        }
    }
    swap(vec[j],vec[l]);
    return j;
}

template<class T, class Pr>
T select(vector<T> &vec, int l, int r, int k, Pr pred)
{
    int n = r-l+1;
    if (n==1)
    {
        if (k!=0)
            printf("Out of Boundary!
");
        return vec[l];
    }
    int cnt = n/5;
    int tcnt = (n+4)/5;
    int rem = n%5;
    vector<T> group(tcnt);
    int i, j;
    for (i=0,j=l; i<cnt; i++,j+=5)
    {
        insert_sort(vec, j, j+4, pred);
        group[i] = vec[j+2];
    }
    if (rem)
    {
        insert_sort(vec, j, j+rem-1, pred);
        group[i] = vec[j+(rem-1)/2];
    }
    T key = select(group, 0, tcnt-1, (tcnt-1)/2, pred);

    int key_pos = get_position(vec, l, r, key);
    swap(vec[key_pos], vec[l]);
    int pos = partition(vec, l, r, pred);
    int x = pos - l;
    if (x == k) return key;
    else if (x < k)
        return select(vec, pos+1, r, k-x-1, pred);
    else
        return select(vec, l, pos-1, k, pred);
}
double dist(const Point& a, const Point& b)
{
    double x = a.m_x-b.m_x;
    double y = a.m_y-b.m_y;
    return sqrt(x*x+y*y);
}

bool cmpX(const Point& a, const Point& b)
{
    return a.m_x < b.m_x;
}

bool cmpY(const Point& a, const Point& b)
{
    return a.m_y < b.m_y;
}

double minDifferent(vector<Point> p, int l, int r, vector<Point> &result)
{
    if ((r-l+1)==2)
    {
        result[0] = p[l];
        result[1] = p[r];
        if (cmpX(p[r],p[l])) swap(p[l], p[r]);
        return dist(p[l], p[r]);
    }
    if ((r-l+1)==3)
    {
        insert_sort(p, l, r, cmpX);
        double tmp1 = dist(p[l], p[l+1]);
        double tmp2 = dist(p[l+1], p[l+2]);
        double ret = min(tmp1, tmp2);
        if (tmp1 == ret)
        {
            result[0] = p[l];
            result[1] = p[l+1];
        }
        else
        {
            result[0] = p[l+1];
            result[1] = p[l+2];
        }
        return ret;
    }
    int mid = (r+l)>>1;
    Point median = select(p, l, r, mid-l, cmpX);
    vector<Point> res1(2), res2(2);
    double min_l = minDifferent(p, l, mid, res1);
    double min_r = minDifferent(p, mid+1, r, res2);
    double minum = min(min_l, min_r);
    if (minum == min_l)
    {
        result[0] = res1[0];
        result[1] = res1[1];
    }
    else
    {
        result[0] = res2[0];
        result[1] = res2[1];
    }
    vector<Point> yvec;
    int i, j;
    for (i=mid+1; i<=r; i++)
        if (p[i].m_x - p[mid].m_x < minum)
            yvec.push_back(Point(p[i]));
    for (i=mid; i>=l; i--)
        if (p[mid+1].m_x - p[i].m_x < minum)
            yvec.push_back(Point(p[i]));
    sort(yvec.begin(), yvec.end(), cmpY);
    for (i=0; i<yvec.size(); i++)
    {
        for (j=i+1; j<yvec.size() && yvec[j].m_y-yvec[i].m_y<minum &&
                j<=i+7; j++)
        {
            double delta = dist(yvec[i],yvec[j]);
            if (delta < minum)
            {
                minum = delta;
                result[0] = yvec[i];
                result[1] = yvec[j];
            }
        }
    }
    return minum;
}

int main()
{
    int n, i, j;
    double x, y;
    int k = 0;
    map<int,Point> m;
    vector<Point> result(2);
    vector<Point> input;
    cin >> n;
    for (i=0; i<n; i++)
    {
        cin >> x;
        cin >> y;
        input.push_back(Point(x,y));
        m.insert(pair<int,Point>(k,Point(x,y)));
        k++;
    }
    double minum = minDifferent(input, 0, input.size()-1, result);

    for(map<int,Point>::iterator it = m.begin();it != m.end();it++)
    {
        if(it->second == result[0])
        {
            cout<<it->first;
        }
        if(it->second == result[1])
        {
            cout<<" "<<it->first;
        }
    }


    return 0;
}