雷达安装

问题描述







Main.java

import java.util.Arrays;
import java.util.Comparator;
import java.util.Scanner;

public class Main {

static int n,d;
static boolean flag;
static Node node[];

public static void main(String[] args) {

    Scanner in = new Scanner(System.in);
    int x,y;
    n = in.nextInt();
    d = in.nextInt();
    if(n==0 && d==0)return;
    flag = true;
    node = new Node[n];
    for(int i=0;i<n;i++) {
        x = in.nextInt();
        y = in.nextInt();
        if(y>d)flag = false;
        else
            node[i] = new Node(x - Math.sqrt(d*d - y*y), x + Math.sqrt(d*d - y*y));
    }
    //按左端点排序
    Comparator<Node>comparator = new MyComparator();
    Arrays.sort(node,comparator);

    if(flag)System.out.println(solve());
    else System.out.println("-1");
    in.close();
}

public static int solve() {
    int ans;double now;
    ans = 1;now = node[0].getRight();
    //若当前线段与目前集合中的线段没有公共点，则新加入一个雷达
    for(int i=1;i<n;i++) {
        if(node[i].getLeft()<=now)  //如果左端点的值小于等于前一个区间的右端点，则不需要新加雷达
            now = Math.min(now, node[i].getRight());
        else {//如果大于,说明该区间与之前的区间不存在公共部分,则需要新加雷达
            ++ans;
            now = node[i].getRight();
        }
    }
    return ans;
}

}

class MyComparator implements Comparator{

public int compare(Node o1, Node o2) {     //升序
    if(o1.getLeft() > o2.getLeft())
        return 1;
    else if(o1.getLeft() == o2.getLeft())
        return 0;
    else return -1;
}

}

Node.java

public class Node {

private double left;
private double right;

public Node(double left,double right){
    this.left = left;
    this.right = right;
}


public double getLeft() {
    return left;
}


public void setLeft(double left) {
    this.left = left;
}


public double getRight() {
    return right;
}


public void setRight(double right) {
    this.right = right;
}

}