HDU 1007 平面最近点对（计算集几何）

#include<iostream>
#include<cstring>
#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;
#define size 100000
struct pint{double x, y;} jeo[size];
bool cmpx(const int &a, const int &b){return jeo[a].x < jeo[b].x;}
bool cmpy(const int &a, const int &b){return jeo[a].y < jeo[b].y;}
double dis(int &a, int &b)
{
return sqrt((jeo[a].x - jeo[b].x) * (jeo[a].x - jeo[b].x) + (jeo[a].y - jeo[b].y) * (jeo[a].y - jeo[b].y));
}
int n, idx[size], idy[size];
double judge(int l, int r)
{
if (r - l == 1) return dis(idx[l], idx[r]);
if (r - l == 2)
return min(dis(idx[l], idx[l + 1]), min(dis(idx[l + 1], idx[l + 2]), dis(idx[l + 2], idx[l])));
int mid = (l + r) >> 1;
double ans = min(judge(l, mid), judge(mid + 1, r));
int num = 0;
for(int i = l; i <= r; i++)
if (jeo[idx[i]].x >= jeo[idx[mid]].x - ans && jeo[idx[i]].x <= jeo[idx[mid]].x + ans)
idy[num++] = idx[i];
sort(idy, idy + num, cmpy);
for(int i = 0; i < num; i++)
for(int j = i + 1; j < num; j++)
{
if (jeo[idy[j]].y - jeo[idy[i]].y >= ans) break;
ans = min(ans, dis(idy[j], idy[i]));
}
return ans;
}
int main()
{
while(scanf("%d", &n) && n)
{
for(int i = 0; i < n && scanf("%lf%lf", &jeo[i].x, &jeo[i].y); i++)
idx[i] = i;
sort(idx, idx + n, cmpx);
printf("%.2f\n", judge(0, n - 1) * 0.5);
}
return 0;
}