uva-2519 - Radar Installation

反正每一个岛都要有雷达覆盖,放雷达的时候尽可能多覆盖岛......

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cmath>
#include<cstring>
using namespace std;
struct node
{
    double x,y;
};
bool cmp(node a,node b)
{
    return a.x<b.x;
}
int main()
{
       // freopen("in","r",stdin);
        int T,i,n,ans,jishu=0;
        double d,pr,l,r,t;
        node box[1010];
        while(cin>>n>>d)
        {
            if(n==0&&d==0)
                break;
            for(i=0;i<n;i++)
                cin>>box[i].x>>box[i].y;
            sort(box,box+n,cmp);
            t=sqrt((d+box[0].y)*(d-box[0].y));
            pr=box[0].x+t;
            ans=1;
            for(i=0;i<n;i++)
            {
                if(d<fabs(box[i].y))
                {
                    ans=-1;
                    break;
                }
                t=sqrt((d+box[i].y)*(d-box[i].y));
                l=box[i].x-t;
                r=box[i].x+t;
                if(l>pr)
                {
                    pr=r;
                    ans++;
                }
                else if(r<pr)
                    pr=r;
            }
            printf("Case %d: %d\n",++jishu,ans);
        }
}

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.

Input 

The input consists of several test cases. The first line of each case contains two integers n (1n1000) 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

uva-2519 - Radar Installation

原文：http://blog.csdn.net/stl112514/article/details/40481911