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