详细看y总写法 https://www.acwing.com/solution/content/1061/

结论：求线段最少需要几个点可以选到全部全部线段

对于每个岛屿有一个线段上的任意雷达都可以覆盖
对于每一个岛屿都一个线段区间，求解最少雷达覆盖就转换为了
最少选择多少个点可以将线段都取到

import java.util.*;

public class Main {
    static final int N = 1010;
    static ArrayList<double[]> list = new ArrayList<>();
    static int n, d;

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        n = sc.nextInt();
        d = sc.nextInt();

        for (int i = 0; i < n; i++) {
            int x = sc.nextInt(), y = sc.nextInt();
            if (Math.abs(y) > d) {
                System.out.println(-1);
                return;
            }
            double len = Math.sqrt(d * d - y * y);
            list.add(new double[]{x - len, x + len});
        }

        list.sort(Comparator.comparingDouble((o) -> o[1]));

        int ans = 1;
        double cur = list.get(0)[1];
        for (int i = 1; i < list.size(); i++) {
            double[] j = list.get(i);
            if (j[0] > cur) {
                ans ++;
                cur = j[1];
            }
        }

        System.out.println(ans);
    }
}