hdu3511 圆的扫描线

http://blog.csdn.net/firenet1/article/details/47041145

#include <iostream>
#include <algorithm>
#include <string.h>
#include <cmath>
#include <cstdio>
#include <set>
using namespace std;
const int maxn=;
struct Circle
{
    int id,x,y,r;
    Circle(int cid=,int cx=,int cy=,int cr=)
    {
         id=cid; x=cx; y=cy; r=cr;
    }
}cir[maxn],P[maxn];

bool cmp(Circle a, Circle b)
{
    return a.x<b.x;
}
int globalx;
struct point{
  int id,ty;
  point(int cid=, int cty=){
      id=cid;
      ty=cty;
  }
};
double yposition(int id, int ty)
{
    double x=globalx-cir[id].x;
    double y=sqrt(1.0*cir[id].r*cir[id].r-x*x);
    if(ty==)return cir[id].y+y;
    return cir[id].y-y;
}
bool operator <(point a, point b)
{
     if(a.id==b.id)return a.ty>b.ty;
     return yposition(a.id,a.ty)>yposition(b.id,b.ty);
}
bool operator == (point a, point b)
{
     return a.id==b.id&&a.ty==b.ty;
}

set<point>Q;
int dep[maxn];
int main()
{
   int n;
    while(scanf("%d",&n)==)
        {
            Q.clear();
             int cnt=;
             for(int i=; i<n; i++)
                {
                     scanf("%d%d%d",&cir[i].x,&cir[i].y, &cir[i].r);
                     cir[i].id=i;
                     P[cnt++]=Circle(i,cir[i].x-cir[i].r,);
                     P[cnt++]=Circle(i,cir[i].x+cir[i].r,);
                }
                sort(P,P+cnt,cmp);
               memset(dep,,sizeof(dep));
               set<point>:: iterator it1,it2;
               int ans=;
               for(int i=; i<cnt; i++)
                {
                    globalx=P[i].x;
                     if(P[i].y==)
                        {
                             Q.erase(point(P[i].id,));
                             Q.erase(point(P[i].id,));
                        }else
                        {
                            it1=Q.insert(point(P[i].id,)).first;
                            it2=it1;
                            it1++;
                            if(it1==Q.end()||it2==Q.begin()){
                                dep[ P[i].id] =;
                            }else
                            {
                                 it2--;
                                 if(it1->id==it2->id){
                                    dep[P[i].id]=dep[it1->id]+;
                                 }else
                                 {
                                    dep[P[i].id]=max(dep[it1->id],dep[it2->id]);
                                 }
                            }

                            Q.insert(point(P[i].id,));

                        }
                        ans=max(dep[P[i].id],ans);
                }
                printf("%d\n",ans);
        }
    return ;
}