POJ 2653 Pick-up sticks 线段相交问题

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <queue>
using namespace std;
#define INF 0x3f3f3f3f
#define eps 1e-8
const 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-p0.x)*(p2.y-p0.y) - (p2.x-p0.x)*(p1.y-p0.y);
}
int line_in_line(Line L1, Line L2)  //线段相交 (包含交点)
{
    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%lf%lf%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%lf%lf%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]);
    }
}

line_in_line()函数也可以这么写:

int line_in_line(Line L1, Line L2)  //线段相交 (包含交点)
{
//    矩阵跨立
    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) ;
}

我奇怪之前我写的为什么会超时.

代码.我用判断visit优化了.知道的给个回复:

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <queue>
using namespace std;
#define INF 0x3f3f3f3f
#define eps 1e-8
const 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);
    }
}