poj 2653 Pick-up sticks 线段相交判断

http://poj.org/problem?id=2653

顺序的在地上扔一些细棒，求最后没有被压的细棒。

我是用list容器存储，枚举过去，有被压的就删除，效率比较底，运行800多ms。

 

#include<stdio.h>

#include<stdlib.h>

#include<string.h>

#include<iostream>

#include<cmath>

#include<list>

using namespace std;

struct point

{

double x,y;

};

struct line

{

point a,b;

int num;

};

list<line> dlist;

double multi(point p0,point p1,point p2)

{

return (p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y);

}

 

bool is(point s1,point e1,point s2,point e2) //判断线段是否相交 

{

return (max(s1.x,e1.x)>=min(s2.x,e2.x))&&

  (max(s2.x,e2.x)>=min(s1.x,e1.x))&&

  (max(s1.y,e1.y)>=min(s2.y,e2.y))&&

  (max(s2.y,e2.y)>=min(s1.y,e1.y))&&

  (multi(s1,s2,e1)*multi(s1,e1,e2)>=0)&&

  (multi(s2,s1,e2)*multi(s2,e2,e1)>=0);

}

double dis(point p1,point p2)

{

return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));

}

int main()

{

int n,i;

line in;

list<line>::iterator iter1,iter2;

while(scanf("%d",&n),n)

{

for(i=0;i<n;i++)

{

scanf("%lf%lf%lf%lf",&in.a.x,&in.a.y,&in.b.x,&in.b.y);

in.num=i+1;

dlist.push_back(in);

}

for(iter1=dlist.begin();iter1!=dlist.end();iter1++)

for(iter2=dlist.begin();iter2!=iter1;)

{

if(is((*iter1).a,(*iter1).b,(*iter2).a,(*iter2).b))

iter2=dlist.erase(iter2);

else

iter2++;

}

printf("Top sticks: %d",(*dlist.begin()).num);

for(iter1=++dlist.begin();iter1!=dlist.end();iter1++)

printf(", %d",(*iter1).num);

printf(".\n");

dlist.clear();

}

return 0;

}