UVALive4974 CERC2010B Beasts

思想是半平面交+旋转卡壳，关于X轴取一次对称再求包围(0, -10^10)点的部分后再对称回来可以少写点针对性代码。左右的射线单独处理了。

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<algorithm>
#include<iostream>
#include<math.h>
using namespace std;
const int maxn = 211111;
const double eps = 1e-9;
typedef double PELEM;
typedef long long LL;
struct Point
{
    PELEM x, y;
    Point()
    {
        x = y = 0;
    }
    Point(PELEM a, PELEM b)
    {
        x = a, y = b;
    }
    PELEM cross(const Point &b, const Point &c)const
    {
        return (b.x - x) * (c.y - y)
               - (c.x - x) * (b.y - y);
    }
    PELEM dot(const Point &p)const
    {
        return x * p.x + y * p.y;
    }
    Point operator-(const Point &p)const
    {
        return Point(x - p.x, y - p.y);
    }
    Point operator+(const Point &p)const
    {
        return Point(x + p.x, y + p.y);
    }
    Point operator-()const
    {
        return Point(-x, -y);
    }
} p[2][maxn << 1];
struct Line
{
    LL a, b, c;
    bool operator<(const Line &l)const
    {
        if(a *l.b == b * l.a)
            return l.c * b < c * l.b;
        return a * l.b > b * l.a;
    }
    int CmXL(const Line &l)const
    {
        if(a * l.b < b * l.a) return 1;
        else if(a * l.b > b * l.a) return -1;
        return 0;
    }
    bool paral(const Line &l)const
    {
        return a * l.b == b * l.a;
    }
    bool high(const Point &p)const
    {
        return p.x * a + p.y * b - c > eps;
    }
    Point CrossP(const Line &l)const
    {
        return Point((double)(c * l.b - l.c * b) / (a * l.b - l.a * b),
                     (double)(c * l.a - l.c * a) / (b * l.a - l.b * a));
    }
};
void HPC(Line l[], int n, Point p[], Line nl[], int &pm, int &lm)
{
    int i, tn;
    sort(l, l + n);
    pm = lm = 0;
    nl[lm ++] = l[0];
    for(i = 1; i < n; ++ i)
    {
        if(lm && nl[lm - 1].paral(l[i])) continue;
        while(pm && !l[i].high(p[pm - 1]))
            -- pm, -- lm;
        p[pm ++] = nl[lm - 1].CrossP(l[i]);
        nl[lm ++] = l[i];
    }
    if(pm == 0) p[pm ++] = Point(0, (double)nl[0].c / nl[0].b);
}
int n, pn1, pn2, ln1, ln2;
Line l[maxn], l1[maxn], l2[maxn];
Point p1[maxn], p2[maxn];
Point CrossPoint(Point a, Point b, Point c, Point d)
{
    double u = a.cross(b, c), v = b.cross(a, d);
    return Point((c.x * v + d.x * u) / (u + v), (c.y * v + d.y * u) / (u + v));
}
double DisPtoP(Point a, Point b)
{
    return (a - b).dot(a - b);
}

double DisPtoS(Point p, Point a, Point b, bool mk)
{
    Point t = Point(p.x + a.y - b.y, p.y + b.x - a.x);
    if(mk && (t - a).dot(b - a) > eps || t.cross(a, p) * t.cross(b, p) < -eps)
        return DisPtoP(p, CrossPoint(t, p, a, b));
    return min(DisPtoP(p, a), DisPtoP(p, b));
}
double DisStoS(Point a, Point b, Point c, Point d)
{
    double ans = 1e30;
    ans = min(ans, DisPtoS(a, c, d, 0));
    ans = min(ans, DisPtoS(b, c, d, 0));
    ans = min(ans, DisPtoS(c, a, b, 0));
    ans = min(ans, DisPtoS(d, a, b, 0));
    return ans;
}
int main()
{
    int t, i, j, k;
    double ans;
    Point ts, te;
    for(scanf("%d", &t); t --; )
    {
        ans = 1e30;
        scanf("%d", &n);
        for(i = 0; i < n; ++ i)
        {
            scanf("%lld%lld%lld", &l[i].a, &l[i].b, &l[i].c), l[i].c = -l[i].c;
            if(l[i].b < 0) l[i].a = -l[i].a, l[i].b = -l[i].b, l[i].c = -l[i].c;
        }
        HPC(l, n, p1, l1, pn1, ln1);
        for(i = 0; i < n; ++ i)
            l[i].a = -l[i].a, l[i].c = -l[i].c;
        HPC(l, n, p2, l2, pn2, ln2);
        for(i = 0; i < ln2; ++ i)
            l2[i].a = -l2[i].a, l2[i].c = -l2[i].c;
        for(i = 0; i < pn2; ++ i)
            p2[i].y = -p2[i].y;
        for(i = 0, j = pn2 - 1; i + 1 < pn1 || j;)
        {
            if(j && (i == pn1 - 1 || l1[i + 1].CmXL(l2[j]) == 1))
                ans = min(ans, DisPtoS(p1[i], p2[j - 1], p2[j], 0)), -- j;
            else if(i < pn1 - 1 && (!j || l1[i + 1].CmXL(l2[j]) == -1))
                ans = min(ans, DisPtoS(p2[j], p1[i], p1[i + 1], 0)), ++ i;
            else
            {
                ans = min(ans, DisStoS(p1[i], p1[i + 1], p2[j - 1], p2[j]));
                ++ i, -- j;
            }
        }
        ts = Point(p2[0].x - 1, (l2[0].c - l2[0].a * (p2[0].x - 1)) / l2[0].b);
        te = Point(p2[pn2 - 1].x + 1, (l2[pn2].c - l2[pn2].a * (p2[pn2 - 1].x + 1)) / l2[pn2].b);
        for(i = 0; i < pn1; ++ i)
        {
            ans = min(ans, DisPtoS(p1[i], p2[0], ts, 1));
            ans = min(ans, DisPtoS(p1[i], p2[pn2 - 1], te, 1));
        }
        ts = Point(p1[0].x - 1, (l1[0].c - l1[0].a * (p1[0].x - 1)) / l1[0].b);
        te = Point(p1[pn1 - 1].x + 1, (l1[pn1].c - l1[pn1].a * (p1[pn1 - 1].x + 1)) / l1[pn1].b);
        for(i = 0; i < pn2; ++ i)
        {
            ans = min(ans, DisPtoS(p2[i], p1[0], ts, 1));
            ans = min(ans, DisPtoS(p2[i], p1[pn1 - 1], te, 1));
        }
        printf("%.6f\n", ans);
    }
    return 0;
}