POJ 2653 Pick-up sticks(计算几何 求交点)

题意：依次给你n根棍子，问最上面的棍子是哪几根。

直接暴力，TLE，，用一个双向链表优化 500ms

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <cmath>#include <queue>using namespace std;const double EPS = 1e-6;const double INF = 1e20;struct cvector{    double x,y;    cvector(double a,double b){x=a,y=b;}    cvector(){}};cvector operator+(cvector a,cvector b){    return cvector(a.x+b.x,a.y+b.y);}cvector operator-(cvector a,cvector b){    return cvector(a.x-b.x,a.y-b.y);}cvector operator*(double a,cvector b){    return cvector(a*b.x,a*b.y);}double operator*(cvector a,cvector b){    return a.x*b.x+a.y*b.y;}double operator^(cvector a,cvector b){    return a.x*b.y-b.x*a.y;}double length(double t){return t>0?t:-t;}double length(cvector t){return sqrt(t*t);}struct cpoint{    double x,y;    cpoint(double a,double b){x=a,y=b;}    cpoint(){}};cvector operator-(cpoint a,cpoint b){    return cvector(b.x-a.x,b.y-a.y);}double dist(cpoint a,cpoint b){    return length(b-a);}struct cline{    cpoint a,b;};bool intersect(cline a,cline b){    return ((a.a-b.a)^(b.b-b.a))*((a.b-b.a)^(b.b-b.a))<EPS&&((b.a-a.a)^(a.b-a.a))*((b.b-a.a)^(a.b-a.a))<EPS;}const int N = 100009;int ans[N];cline line[N];int fron[N],nex[N];int main(){    freopen("in.txt","r",stdin);    int n;    while(~scanf("%d",&n)&&n)    {        for(int i=1;i<=n;i++)        {            ans[i] = 1;nex[i] = i-1;fron[i-1] = i;            scanf("%lf%lf%lf%lf",&line[i].a.x,&line[i].a.y,&line[i].b.x,&line[i].b.y);            for(int j=i-1;j>0;)            {                if(ans[j]&&intersect(line[j],line[i]))                {                    nex[fron[j]] = nex[j];                    fron[nex[j]] = fron[j];                    ans[j] = 0;                }                j = nex[j];            }        }        fron[n] = n+1;        printf("Top sticks: ");        bool ou = false;        for(int i=fron[0];i<=n;)        {            if(ou) printf(", ");ou = true;            printf("%d",i);            i=fron[i];        }        printf(".\n");    }    return 0;}