poj 1328 Radar Installation

http://poj.org/problem?id=1328

题意：在一个海岸线上按一些雷达，是雷达可以覆盖海面的小岛，问最少安装多少雷达；

思路：快拍+贪心；

代码：

#include <stdio.h>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <cstdlib>
#include <string.h>
#include <cmath>
using namespace std;
struct node
{
    double l;
    double r;
}link[1001];
int num = 0;
double len = 0;
int cmp(node a,node b)
{
    return a.l <b.l;
}
int main()
{
    double a = 0,b = 0;
    int time = 0;
    while(scanf("%d%lf",&num,&len),num != 0&&len != 0)
    {
        ++time;
        int biao = 0;
         double dd = 0;
    int nu = 1;
        for(int i = 0; i < num ;++i)
        {
        scanf("%lf%lf",&a,&b);
        if(b > len)
        biao = 1;
        link[i].l = a - sqrt(len *len - b * b);
        link[i].r = a + sqrt(len *len - b * b);
        }
        if(biao)
        {
            printf("Case %d: -1\n",time);
            continue;
        }
        sort(link,link+num,cmp);
        dd = link[0].r;
        for(int i = 1; i <num; ++i)
        {
            if(link[i].l <= dd)
            dd = min(link[i].r,dd);
            else
            {
            nu++;
            dd = link[i].r;
            }
        }
        printf("Case %d: %d\n",time,nu);
    }
    return 0;
}