hdu 1558 Segment set

http://acm.hdu.edu.cn/showproblem.php?pid=1558

先判断线段相交，然后用并查集合并。

#include <cstdio>
#include <cstring>
#include <algorithm>
#define maxn 20000
using namespace std;

int num[maxn],f[maxn];

struct point
{
    double x,y;
};
struct line
{
    point p1,p2;
}p[maxn];


void inti()
{
    for(int i=0; i<=maxn; i++)
    {
        f[i]=i;
        num[i]=1;
    }
}
double det(point a,point b,point c)
{
    return (c.x-a.x)*(b.y-a.y)-(c.y-a.y)*(b.x-a.x);
}

int find1(int x)
{
    if(x==f[x]) return x;
    return f[x]=find1(f[x]);
}

void merge1(int a,int b)
{
    int fa=find1(a);
    int fb=find1(b);
    if(fa!=fb)
    {
        f[fa]=fb;
        num[fb]+=num[fa];
    }
}

bool Isintsert(line u,line v)
{
    return (det(v.p1,u.p2,u.p1)*det(u.p2,v.p2,u.p1)>=0)&&(det(u.p1,v.p2,v.p1)*det(v.p2,u.p2,v.p1)>=0)&&
    (max(u.p1.x,u.p2.x)>=min(v.p1.x,v.p2.x))&&
    (max(v.p1.x,v.p2.x)>=min(u.p1.x,u.p2.x))&&
    (max(u.p1.y,u.p2.y)>=min(v.p1.y,v.p2.y))&&
    (max(v.p1.y,v.p2.y))>=min(u.p1.y,u.p2.y);
}

int main()
{
    int t,n,k1;
    char ch;
    scanf("%d",&t);
    while(t--)
    {
        inti();
        scanf("%d",&n);
        getchar();
        int t1=1;
        for(int i=0; i<n; i++)
        {
            scanf("%c",&ch);
            if(ch=='P')
            {
                scanf("%lf%lf%lf%lf",&p[t1].p1.x,&p[t1].p1.y,&p[t1].p2.x,&p[t1].p2.y);
                t1++;
                for(int j=1; j<t1-1; j++)
                {
                    int f2=find1(t1-1); int f3=find1(j);
                    if(f2!=f3&&Isintsert(p[j],p[t1-1]))
                    {
                        merge1(j,t1-1);
                    }
                }
            }
            else if(ch=='Q')
            {
                scanf("%d",&k1);
                int k2=find1(k1);
                printf("%d
",num[k2]);
            }
            getchar();
            
        }
        if(t!=0) printf("
");
    }
    return 0;
}