poj 1328 Radar Installation 【贪心】
2015-07-31 14:48
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Radar Installation
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
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
Sample Output
Time Limit: 1000MS | Memory Limit: 10000K | |
Total Submissions: 64022 | Accepted: 14402 |
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
无语死了,以后除了特殊情况不会在杭电DIY做poj的题目了。经常卡死,代码提交还是空代码。 转战zoj。。。
贪心:求出能够覆盖当前点的 区间[Ai,Bi],按区间右边界 Bi 从小到大排序后, 判断区间是否重叠。
#include <cstdio> #include <cstring> #include <cmath> #include <algorithm> #define INF 100000000 #define DD double using namespace std; struct rec { DD start, end; }; rec num[1010]; bool cmp(rec a, rec b) { return a.end < b.end; } int main() { int N, k = 1; DD d; bool flag; while(scanf("%d%lf", &N, &d), N||d) { DD x, y; flag = true; for(int i = 0; i < N; i++) { scanf("%lf%lf", &x, &y); if(!flag) continue; if(y > d) { flag = false; continue; } num[i].start = x - sqrt(d * d - y * y); num[i].end = x + sqrt(d * d - y * y); } printf("Case %d: ", k++); if(!flag) { printf("-1\n"); continue; } sort(num, num+N, cmp); int ans = 0; DD temp = -INF; for(int i = 0; i < N; i++) { if(temp < num[i].start) ans++, temp = num[i].end; } printf("%d\n", ans); } return 0; }
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