雷达设备

 

#include <bits/stdc++.h>
using namespace std;
const int N = 1010;
const double eps = 1e-6, INF = 1e10;
//eps用于精度判断
typedef pair<double, double> pdd;
pdd segs[N];
int main() {
    int n, r;
    cin >> n >> r;
    for (int i = 0; i < n; i++) {
        int x, y;
        cin >> x >> y;
        if (y > r) {
            cout << -1 << endl;
            return 0;
        }
        double len = sqrt(r * r - y * y);
        segs[i] = {x + len, x - len};
        //需要按照右端点从小到大排序
        //所以first和second交换一下
        //second是起点，first是终点
    }
    sort(segs, segs + n);
    int res = 0;
    double last = -INF;
    //last是上一个雷达的位置，初始化为负无穷
    for (int i = 0; i < n; i++) { //扫描一遍
        if (segs[i].second > last + eps) { //如果当前起点，大于上一个终点
            res++;
            last = segs[i].first;
        }
    }
    cout << res << endl;
    return 0;
}