Radar
时间限制:1000 ms | 内存限制:65535 KB
难度:3
- 描述
- 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.
- 输入
- 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 输出 - 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. 样例输入
-
3 2 1 2 -3 1 2 1 1 2 0 2 0 0
样例输出 -
Case 1: 2 Case 2: 1
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我至今不知道它的输出数据间为什么要空一行······一开始加了就错了,后来去了就过了。思路很简单:找出可以覆盖点的区间范围[start,end],接下来就是区间找点问题。(建议做这道题前做一下nyoj贪心专题里面的891找点和1036非洲小孩)
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#include<stdio.h> #include<math.h> #include<algorithm> using namespace std; struct island { double start; double end; }num[1010]; bool cmp(island a,island b) { return (a.end<b.end); } int main() { int m,i; double r,x,y,max; int exist; int sum; int j=1; while(scanf("%d %lf",&m,&r)&&(m!=0||r!=0)) { exist=1; for(i=0;i<m;i++) { scanf("%lf %lf",&x,&y); num[i].start=x-sqrt(r*r-y*y); num[i].end=x+sqrt(r*r-y*y); if(y>r) { exist=0; break; } } if(exist==0) printf("-1\n"); else { sort(num,num+m,cmp); max=num[0].end; sum=1; for(i=1;i<m;i++) { if(num[i].start>max) { sum++; max=num[i].end; } } printf("Case %d: %d\n",j++,sum); } } return 0; }
- 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.