Assume the coasting is an infinite straight line. Land is in one side of coasting, sea in the other. Each small island is a point locating in the sea side. And any radar installation, locating on the coasting, can only cover d distance, so an island in the sea can be covered by a radius installation, if the distance between them is at most d.
We use Cartesian coordinate system, defining the coasting is the x-axis. The sea side is above x-axis, and the land side below. Given the position of each island in the sea, and given the distance of the coverage of the radar installation, your task is to write a program to find the minimal number of radar installations to cover all the islands. Note that the position of an island is represented by its x-y coordinates.
Figure A Sample Input of Radar Installations
Input
The input consists of several test cases. The first line of each case contains two integers n (1<=n<=1000) and d, where n is the number of islands in the sea and d is the distance of coverage of the radar installation. This is followed by n lines each containing two integers representing the coordinate of the position of each island. Then a blank line follows to separate the cases.
The input is terminated by a line containing pair of zeros
Output
For each test case output one line consisting of the test case number followed by the minimal number of radar installations needed. "-1" installation means no solution for that case.
Sample Input
3 2 1 2 -3 1 2 1 1 2 0 2 0 0
Sample Output
Case 1: 2 Case 2: 1 题目大意：就是给你n组数据和圆的半径d，让你在x轴上画半径为d的圆，问：如果将所有的点都画进去，最少需要多少个圆，这个题目和导弹拦截有点像，不过更加简单 思路：就是先判断d是不是大于等于0，如果d<0，肯定是输出-1的，之后输入数字，如果有坐标的纵坐标比d还要大，那么也是不对的也要输出-1之后对坐标进行处理，把每一个坐标在x轴上的范围标记出来，并进行排序，先排右边的位置，右边位置越小就排在越前面，因为我们是要从横坐标左边往右边排如果右边相同，就排左边，左边大的先排，因为区间范围小的肯定可以把区间范围大的包括进去，反之则不行。排完序之后就开始画圈圈。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <algorithm>
#include <math.h>
#include <iostream>
using namespace std;
const int maxn=1010;
struct node
{
double l,r;
}exa[maxn];
bool cmp(node a,node b)
{
if(a.r==b.r) return a.l>b.l;
return a.r<b.r;
}
int main()
{
int n,cnt=0;;
double d,a,b;
while(scanf("%d%lf",&n,&d)!=EOF&&(n+d))
{
bool flag=0;
if(d>=0) flag=1;
for(int i=0;i<n;i++)
{
scanf("%lf%lf",&a,&b);
if(b>d) flag=0;
if(flag)
{
exa[i].l=a-sqrt(d*d-b*b);
exa[i].r=a+sqrt(d*d-b*b);
}
}
sort(exa,exa+n,cmp);
int ans=-1;
if(flag)
{
ans=1;
double maxr=exa[0].r;
for(int i=1;i<n;i++)
{
if(exa[i].l>maxr)
{
ans++;
maxr=exa[i].r;
}
}
}
cout << "Case " << ++cnt << ": " << ans << endl;
}
return 0;
}
原文地址：https://www.cnblogs.com/EchoZQN/p/10359199.html