OJ-Problems-Source/HDOJ/3867_autoAC.cpp
2016-09-04 14:17:41 +08:00

106 lines
3.1 KiB
C++

#include <cstdio>
#include <cstring>
#include <cmath>
#include <set>
#include <algorithm>
using namespace std;
#define EPS 1e-8
#define LS0(a) (a << 1)
#define LS1(a) ((a << 1) | 1)
const int MAXN = 20010;
struct Point {
double x, y;
Point(double _x = 0.0, double _y = 0.0): x(_x), y(_y) {}
Point operator + (const Point &b) const {
return Point(x + b.x, y + b.y);
}
Point operator - (const Point &b) const {
return Point(x - b.x, y - b.y);
}
double operator ^ (const Point &b) const {
return x * b.y - y * b.x;
}
bool operator < (const Point &b) const {
return x * b.y < y * b.x;
}
void input() {
scanf("%lf%lf", &x, &y);
}
double diso() {
return sqrt(x * x + y * y);
}
}cur,ps[MAXN];
Point lnlncross_pt(Point aa, Point ad, Point ba, Point bd) {
ad = ad - aa;
bd = bd - ba;
double tmp = bd ^ ad;
return Point(
(ad.x * bd.x * (ba.y - aa.y) + aa.x * bd.x * ad.y - ba.x * ad.x * bd.y) / tmp,
(ad.y * bd.y * (aa.x - ba.x) + ba.y * ad.y * bd.x - aa.y * bd.y * ad.x) / tmp);
}
struct Item {
Point *u, *v;
int type;
int sgid;
Item(Point *_u = NULL, Point *_v = NULL, int _ty = 0, int _id = 0)
: u(_u), v(_v), type(_ty), sgid(_id) {}
bool operator < (const Item &b) const {
if(u == b.u && v == b.v)
return false;
Point au = lnlncross_pt(Point(0.0, 0.0), cur, *u, *v);
Point bu = lnlncross_pt(Point(0.0, 0.0), cur, *b.u, *b.v);
return au.diso() < bu.diso();
}
}item[MAXN];
bool flag[MAXN];
set<Item> Scan;
bool cmp(const Item &a, const Item &b) {
return atan2(a.u->y, a.u->x) < atan2(b.u->y, b.u->x);
}
void inputps(int n) {
Point src, a, b;
src.input();
for(int i = 0; i < n; ++i) {
a.input(); a = a - src;
b.input(); b = b - src;
if(b < a) swap(a, b);
ps[LS0(i)] = a;
ps[LS1(i)] = b;
item[LS0(i)] = Item(&ps[LS0(i)], &ps[LS1(i)], 0, i);
item[LS1(i)] = Item(&ps[LS1(i)], &ps[LS0(i)], 1, i);
}
sort(item, item + 2 * n, cmp);
}
bool sgcross_with_ax(Item &a) {
Point tmp(-1.0, 0.0);
return (*a.u ^ *a.v) * (*a.u ^ tmp) > 0.0
&& (*a.u ^ tmp) * (tmp ^ *a.v) > 0.0;
}
int main() {
int n;
while(scanf("%d", &n) != EOF) {
inputps(n);
memset(flag,0,sizeof(flag));
Scan.clear();
for(int i = 0; i < 2 * n; ++i) {
cur = *item[i].u;
if(item[i].type == 1 && sgcross_with_ax(item[i]))
Scan.insert(item[i]);
}
for(int i = 0; i < 2 * n; ++i) {
cur = *item[i].u;
if(item[i].type == 1)
Scan.insert(item[i]);
else
Scan.erase(Item(item[i].v, item[i].u, 1, item[i].sgid));
if(!Scan.empty())
flag[Scan.begin()->sgid] = true;
}
int ans = 0;
for(int i = 0; i < n; ++i)
if(flag[i])ans ++;
printf("%d\n", ans);
}
return 0;
}