POJ1328 radar installation (Greedy)

//主要是以岛为圆心画圆求区间,还有就是区间交并的问题#include <iostream>#include <cstring>#include <cstdio>#include <cmath>#include <algorithm>using namespace std;int n,d,cas;struct node{    double x,y;    double l,r;}p[1009];bool cmp(node a,node b){    //if(fabs(a.l-b.l)<1e8) return a.r<b.r;    return a.l<b.l;}int main(){    while(scanf("%d%d",&n,&d)){        if(!(n+d)) return 0;        double mx=0;        for(int i=0;i<n;i++){            scanf("%lf%lf",&p[i].x,&p[i].y);            mx=max(mx,p[i].y);        }        if(mx>d){            printf("Case %d: -1\n",++cas);            continue;        }        for(int i=0;i<n;i++){            p[i].l=p[i].x-sqrt(d*d-p[i].y*p[i].y);            p[i].r=p[i].x+sqrt(d*d-p[i].y*p[i].y);        }        sort(p,p+n,cmp);        int cnt=1;        double r=p[0].r;        for(int i=1;i<n;i++){            if(p[i].l>r){                cnt++;r=p[i].r;            }            else if(p[i].r<r)//不能反了,否则i这点有可能没覆盖到                r=p[i].r;        }        printf("Case %d: %d\n",++cas,cnt);    }    return 0;}