HDOJ 1007

HDOJ 1007
二分法

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cmath>
#include<iomanip>
#include<cfloat>
using namespace std;
struct pp {
    double x, y;
};
pp ppt[100010];
pp ppu[100010];
bool qq(pp a,pp b){
    if (a.x != b.x)
        return a.x < b.x;
    else return a.y < b.y;
}
bool qqq(pp a, pp b) {
    return a.y < b.y;
}
double heng(int a, int b)
{
    int mid = (a + b) / 2;
    int i = 0;
    if (a == b)
        return DBL_MAX;
    if (b - a == 1) {
        return sqrt((ppt[a].x - ppt[b].x)*(ppt[a].x - ppt[b].x) + (ppt[a].y - ppt[b].y)*(ppt[a].y - ppt[b].y));
    }
    double aa = heng(a, mid);
    double bb = heng(mid, b);
    double d = min(aa, bb);
    int num = 0;
    for (int i = a;i < b;i++) {
        if (fabs(ppt[mid].x - ppt[i].x) <= d) {
            ppu[num++] = ppt[i];
        }
    }
    sort(ppu, ppu + num, qqq);
    for (int i = 0;i < num;i++) {
        for (int j = i+1;j < num&&ppu[j].y - ppu[i].y <= d;j++) {
            d = min(d, sqrt((ppu[i].x - ppu[j].x)*(ppu[i].x - ppu[j].x) + (ppu[i].y - ppu[j].y)*(ppu[i].y - ppu[j].y)));
        }
    }
    return d;
}
int main()
{
    int a;
    while (cin >> a&&a != 0) {
        for (int i = 0;i < a;i++)
        {
            scanf("%lf%lf", &ppt[i].x , &ppt[i].y);
        }
        sort(ppt, ppt + a, qq);
        printf("%.2lf\n", heng(0, a - 1) / 2);
    }
    return 0;
}