hdu 1007 Quoit Design (最近点对、分治)

#include "stdio.h"
#include "cmath"
#include "iostream"
#include "algorithm"
using namespace std;

struct point {double x, y;};
point p[100003];
point tp[100003];

bool cmp_x(const point & a, const point & b) { return a.x < b.x; }

bool cmp_y(const point & a, const point & b) { return a.y < b.y; }

double min(double a, double b) { return a < b ? a : b; }

double dis(const point & a, const point & b)
{
return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}

double solve(int lf, int rt, int n)  //left, right
{
if(lf == rt) return 1e9;  //只有一个点时，距离设为无穷大
if(rt - lf == 1)
return dis(p[lf], p[rt]);

int mid = (lf + rt) >> 1;
double ans = min(solve(lf, mid, n), solve(mid + 1, rt, n));

int lp = 0, i, j;
for(i = mid; i >= lf && p[i].x - p[mid].x < ans; i--)
{
tp[lp].x = p[i].x;
tp[lp++].y = p[i].y;
}

for(i = mid + 1; i <= rt && p[i].x - p[mid].x < ans; i++)
{
tp[lp].x = p[i].x;
tp[lp++].y = p[i].y;
}

sort(tp, tp + lp, cmp_y);

for(i = 0; i < lp; i++)
for(j = i + 1; j - i < 7 && j < lp; j++)
ans = min(ans, dis(tp[i], tp[j]));

return ans;
}

int main()
{
int n, i;
while(scanf("%d", &n) && n)
{
for(i = 1; i <= n; i++)
scanf("%lf%lf", &p[i].x, &p[i].y);

sort(p + 1, p + n + 1, cmp_x);
printf("%.2lf\n", solve(1, n, n) / 2.0);
}
return 0;
}