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POJ1328 Radar Installation 【贪心·区间选点】
Radar Installation
Time Limit: 1000MS | Memory Limit: 10000K | |
Total Submissions: 54593 | Accepted: 12292 |
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 2 1 2 -3 1 2 1 1 2 0 2 0 0
Sample Output
Case 1: 2 Case 2: 1
Source
Beijing 2002
#include <stdio.h> #include <string.h> #include <math.h> #include <algorithm> #define maxn 1010 using namespace std; struct Node { double u, v; friend bool operator<(const Node& a, const Node& b) { return a.u < b.u; } } E[maxn]; int N, D; int main() { int i, ok, id, ans, cas = 1; double x, y, d, flag; while(scanf("%d%d", &N, &D), N) { printf("Case %d: ", cas++); ok = 1; id = 0; for(i = 0; i < N; ++i) { scanf("%lf%lf", &x, &y); if(y > D) ok = 0; if(!ok) continue; d = sqrt(D * D - y * y); E[id].u = x - d; E[id++].v = x + d; } if(!ok) { printf("-1\n"); continue; } sort(E, E + id); flag = E[0].v; ans = 1; for(i = 1; i < N; ++i) { if(E[i].u <= flag) { if(E[i].v <= flag) flag = E[i].v; continue; } ++ans; flag = E[i].v; } printf("%d\n", ans); } return 0; }
POJ1328 Radar Installation 【贪心·区间选点】
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