Poj 2653 pick-up sticks line segment intersection Problem

# Include <iostream> # include <cstdio> # include <cstdlib> # include <cstring> # include <cmath> # include <algorithm> # include <queue> using namespace STD; # define INF 0x3f3f3f # define EPS 1e-8const int maxn = 100000 + 3; struct point {Double X; Double Y ;}; struct line {Point U; point v ;} stick [maxn]; int visit [1000]; int sig (Double X) {return (x> EPS)-(x <-EPS);} double mult (point P0, point P1, point P2) {return (p1.x-converted X) * (p2.y-converted y)-(p2.x-converted X) * (p1.y-converted y);} int line_in_line (line L1, line l2) // intersection of line segments (including intersections) {If (SIG (mult (l1.u, l2.u, l1.v) * sig (mult (l1.u, l2.v, l1.v )) <= 0 & sig (mult (l2.u, l1.u, l2.v) * sig (mult (l2.u, l1.v, l2.v) <= 0) return 1; return 0 ;} int main () {# ifndef online_judge freopen ("in", "r", stdin); # endif int N, top; while (scanf ("% d", & N) & N) {scanf ("% lf", & Stick [1]. u. x, & Stick [1]. u. y, & Stick [1]. v. x, & Stick [1]. v. y); visit [Top = 1] = 1; for (INT I = 2; I <= N; I ++) {scanf ("% lf", & Stick [I]. u. x, & Stick [I]. u. y, & Stick [I]. v. x, & Stick [I]. v. y); For (Int J = 1; j <= top; j ++) {If (line_in_line (stick [I], stick [visit [J]) {visit [J] =-1 ;}} int cur = 0; For (Int J = 1; j <= top; j ++) {If (visit [J]> 0) visit [++ cur] = visit [J];} Top = cur; visit [++ top] = I ;} printf ("top sticks:"); For (INT I = 1; I <top; I ++) {printf ("% d,", visit [I]);} printf ("% d. \ n ", visit [Top]);}

The line_in_line () function can also be written as follows:

Int line_in_line (line L1, line l2) // intersection of line segments (including intersections) {// return (max (l1.u. x, l1.v. x)> = min (l2.u. x, l2.v. x) & MAX (l2.u. x, l2.v. x)> = min (l1.u. x, l1.v. x) & MAX (l1.u. y, l1.v. y)> = min (l2.u. y, l2.v. y) & MAX (l2.u. y, l2.v. y)> = min (l1.u. y, l1.v. y) & mult (l1.u, l2.v, l2.u) * mult (l2.v, l1.v, l2.u)> = 0 & mult (l2.u, l1.v, l1.u) * mult (l1.v, l2.v, l1.u)> = 0 );}

I wonder why I wrote it out.

Code. I used visit to judge whether it was optimized. I would like to give a reply:

#include <iostream>#include <cstdio>#include <cstdlib>#include <cstring>#include <cmath>#include <algorithm>#include <queue>using namespace std;#define INF 0x3f3f3f3f#define eps 1e-8const int maxn = 100000+3;struct Point{    double x;    double y;};struct Line{    Point u;    Point v;}stick[maxn];bool visit[maxn];int Sig(double x){    return (x>eps) - (x<-eps);}double Mult(Point p0, Point p1, Point p2){    return (p1.x-p0.x)*(p2.y-p0.y) - (p2.x-p0.x)*(p1.y-p0.y);}int line_in_line(Line L1, Line L2){    if(Sig(Mult(L1.u,L2.u,L1.v))*Sig(Mult(L1.u,L2.v,L1.v))<=0 && Sig(Mult(L2.u,L1.u,L2.v))*Sig(Mult(L2.u,L1.v,L2.v)) <=0)        return 1;    return 0;}int main(){#ifndef ONLINE_JUDGE    freopen("in","r",stdin);#endif    int n;    while(scanf("%d",&n) && n)    {        memset(visit, false, sizeof(visit));        for(int i = 1; i <= n; i++)        {            scanf("%lf%lf%lf%lf",&stick[i].u.x,&stick[i].u.y,&stick[i].v.x,&stick[i].v.y);            for(int j = 1; j < i; j++)            {                if(!visit[j] && line_in_line(stick[i],stick[j]))                    visit[j] = true;            }        }        printf("Top sticks:");        for(int i = 1; i< n; i++)        {            if(!visit[i])                printf(" %d,",i);        }        printf(" %d.\n",n);    }}