poj 1328 Radar Installation

#include <iostream>
#include <math.h>
#include<algorithm>
using namespace std;
struct seg 
{
    double left;double right;
    bool operator<(const seg& a)const
    {
        return left<a.left;
    }
}range[1001];

int main()
{
    int n,d,i,t=1;double x,y;bool tag;
    while(cin>>n>>d)
    {
        if(n==0&&d==0)break;
        tag=0;
        for(i=0;i<n;i++)
        {
            cin>>x>>y;
            if(y>d)        
                tag=1;
            if(!tag)    //对于某点（x,y）在x轴上(left,right)的范围内都可以覆盖该点
                range[i].left=x-sqrt(d*d-y*y),range[i].right=x+sqrt(d*d-y*y);
        }
        if(tag==1)
            cout<<"Case "<<t++<<": -1\n";
        else
        {
            sort(range,range+n);        //按左端点从小到大排序
            int count=1;double r=range[0].right;
            for(i=1;i<n;i++)            //只有以下两种情况需要需要处理：
            {
                if(range[i].left>r)            
                {
                    count++;
                    r=range[i].right;
                }
                else if(range[i].right<r)
                    r=range[i].right;
            }
            cout<<"Case "<<t++<<": "<<count<<"\n";
        }
    }
    return 0;
}