poj 2653 Pick-up sticks (线段相交)

提示：

（小）剪枝，每次用队列来优化，如果之前的被覆盖了，那么不在放进队里，最后统计队里残余的线段。

代码：

#include <iostream>#include <cstdio>#include <algorithm>#include <string.h>#include <queue>using namespace std;struct point {    double x,y;};struct line{    point s;//start    point t;//to    int num;}a[100100];int paichi(line a,line b){    if(max(a.s.x,a.t.x)>=min(b.s.x,b.t.x)       &&max(b.s.x,b.t.x)>=min(a.s.x,a.t.x)       &&max(a.s.y,a.t.y)>=min(b.s.y,b.t.y)       &&max(b.s.y,b.t.y)>=min(a.s.y,a.t.y))        return 1;    else return 0;}double cross(point a,point b,point c){    double x1=b.x-a.x;    double y1=b.y-a.y;    double x2=c.x-a.x;    double y2=c.y-a.y;    return x1*y2-x2*y1;}int kuali(line a,line b){    if(cross(a.s,a.t,b.s)*cross(a.s,a.t,b.t)<=0       && cross(b.s,b.t,a.s)*cross(b.s,b.t,a.t)<=0)       return 1;    return 0;}int vis[100100];int main(){    int n;    while(scanf("%d",&n),n){        memset(vis,0,sizeof(vis));        scanf("%lf%lf%lf%lf",&a[1].s.x,&a[1].s.y,&a[1].t.x,&a[1].t.y);a[1].num = 1;        queue<line> q;q.push(a[1]);        for(int i = 2;i <= n;i++){            scanf("%lf%lf%lf%lf",&a[i].s.x,&a[i].s.y,&a[i].t.x,&a[i].t.y);a[i].num = i;            int siz = q.size();line temp;            for(int j = 0;j < siz;j++){                temp = q.front();                q.pop();                if(paichi(a[i],temp) && kuali(a[i],temp)){                }                else                    q.push(temp);            }            q.push(a[i]);        }        int cnt = 0,cnt2 = 0;line temp;        while(!q.empty()){            temp = q.front();            vis[temp.num] = 1;cnt++;            q.pop();        }        printf("Top sticks: ");        for(int i = 1;i <= n;i++){            if(vis[i] == 1){                if(cnt2 == cnt-1)                    printf("%d.\n",i);                else                    printf("%d, ",i);                cnt2++;            }        }    }    return 0;}