POJ-1328
Radar Installation
Time Limit: 1000MS Memory Limit: 10000K Total Submissions: 89640 Accepted: 20135 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 InstallationsInput
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 zerosOutput
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 0Sample Output
Case 1: 2 Case 2: 1
题意:
有n座岛,在x轴上最少建立多少半径为d的雷达可以覆盖所有的岛。
贪心。
首先以岛为圆心,d为半径求出x轴上符合的区间,再将区间按左到右的顺序排序,若当前点的左端点大于之前最大的右端点,则++。更新最右端点。
AC代码:
1 #include<iostream> 2 #include <stdio.h> 3 #include <stdlib.h> 4 #include <string.h> 5 #include <math.h> 6 #include <algorithm> 7 //#include<bits/stdc++.h> 8 using namespace std; 9 10 struct node{ 11 double le,ri; 12 }a[2010]; 13 14 int cmp(node a,node b){ 15 return a.le<b.le; 16 } 17 18 int x[2010],y[2010]; 19 20 int main(){ 21 ios::sync_with_stdio(false); 22 int ans=0; 23 int n,d,num,flag; 24 double z,temp; 25 while(cin>>n>>d){ 26 if(n==0&&d==0) break; 27 ans++; 28 flag=0; 29 for(int i=0;i<n;i++){ 30 cin>>x[i]>>y[i]; 31 if(y[i]>d) 32 flag=1; 33 } 34 if(flag){ 35 cout<<"Case "<<ans<<": -1"<<endl; 36 } 37 else{ 38 for(int i=0;i<n;i++){ 39 z=sqrt(d*d*1.0-y[i]*y[i]*1.0); 40 a[i].le=(double)x[i]-z; 41 a[i].ri=(double)x[i]+z; 42 } 43 sort(a,a+n,cmp); 44 temp=-100000000; 45 num=0; 46 for(int i=0;i<n;i++){ 47 if(a[i].le>temp){ 48 num++; 49 temp=a[i].ri; 50 }else if(a[i].ri<temp){ 51 temp=a[i].ri; 52 } 53 } 54 cout<<"Case "<<ans<<": "<<num<<endl; 55 } 56 } 57 return 0; 58 }