poj 1328
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Radar Installation
Time Limit: 1000MS Memory Limit: 10000KTotal Submissions: 72902 Accepted: 16269
Description
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
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
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 21 2-3 12 11 20 20 0
Sample Output
Case 1: 2Case 2: 1
Source
Beijing 2002
题意:假设海岸线是一条无限延伸的直线。陆地在海岸线的一侧,而海洋在另一侧。每一个小的岛屿是海洋上的一个点。雷达坐落于海岸线上,只能覆盖d距离,所以如果小岛能够被覆盖到的话,它们之间的距离最多为d。
题目要求计算出能够覆盖给出的所有岛屿的最少雷达数目。
我们假设岛屿i它的x坐标为island[i][0],而y坐标为island[i][1],那么有以下几种情况是invalide的,即输出-1的情况:
1.island[i][1]<0
2.abs(island[i][1])<d
3.d<0
其他的情况,应该就是正常情况,进入计算最小雷达数目。
如上图,红色的点为岛屿,那么能够覆盖到此岛屿的雷达所在的区间,应该就是以该岛屿为圆心的圆与x轴交点所在的区间。
这样,我们就可以计算出所有岛屿的雷达所在的区间,得到一个区间数组。
我们将这个数组按照区间左部分进行排序,那么重叠部分就表明这些岛屿的雷达可以共用一个。从而计算出最终解。
#include <string.h>
#include <queue>
#include <stdlib.h>
#include <math.h>
#include <algorithm>
typedef long long LL;
#define max(a,b)(a>b?a:b)
#define min(a,b)(a<b?a:b)
#define N 1005
#define oo 0x3f3f3f3f
using namespace std;
struct point
{
double l,r;
}p[1100];
int cmp(point a,point b)
{
return a.l < b.l ;
}
int main()
{
int n,d,x,y,ca=1,ans,i;
double s;
while(scanf("%d%d",&n,&d),n+d)
{
int f=0;
for(i=0;i<n;i++)
{
scanf("%d%d",&x,&y);
if(y>d )
{
f=1;
}
p[i].l=x-sqrt(1.0*d*d-1.0*y*y);
p[i].r=x+sqrt(1.0*d*d-1.0*y*y);
}
if(f==1)
{
printf("Case %d: -1\n",ca++);
continue;
}
else
{
sort(p,p+n,cmp);
ans=1;
s=p[0].r;
for(i=1;i<n;i++)
{
if(s<p[i].l)
{
s=p[i].r;
ans++;
}
else if(s>p[i].r)
{
s=p[i].r;
}
}
printf("Case %d: %d\n",ca++,ans);
}
}
return 0;
}
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