poj 1328 Radar Installation

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>

using namespace std;

struct node
{
    double x,y;
} a[1005];

struct len
{
    double l, r;
} ans[1005];

bool cmp(len x1, len x2)
{
    if(fabs(x1.l-x2.l)<1e-10)
        return x1.r < x2.r;
    return x1.l < x2.l;
}

int main()
{
    int n;
    double d;
    int k=1;
    while(scanf("%d%lf",&n, &d),n+d)
    {
        int flag = 0;
        for(int i=0; i<n; i++)
        {
            scanf("%lf%lf",&a[i].x,&a[i].y);
            if(a[i].y-d > 1e-10)
            {
                flag = 1;
            }
        }
        int s = 1;
        if(flag)
            s=-1;
        else
        {
            for(int i=0; i<n; i++)
            {
                double l = sqrt(pow(d,2) - pow(a[i].y,2));
                ans[i].l = a[i].x - l;
                ans[i].r = a[i].x + l;
            }
            sort(ans, ans+n, cmp);

            double R = ans[0].r;
            for(int i=1; i<n; i++)
            {
                if(ans[i].l-R > 1e-10)
                {
                    s++;
                    R = ans[i].r;
                }
                else
                {
                    R = min(R, ans[i].r);
                }
            }
        }
        printf("Case %d: %d\n",k++,s);
    }

    return 0;
}