poj 1328 Radar Installation （贪心）

标签：des   style   http   color   os   io   strong   for   ar   

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

Output

Sample Input

3 2
1 2
-3 1
2 1

1 2
0 2

0 0

Sample Output

Case 1: 2
Case 2: 1

这些仔细考率都能过的，因为一个变量搞成int型竟然错了好久！

#include"stdio.h"
#include"string.h"
#include"math.h"
#include"iostream"
#include"algorithm"
using namespace std;
#define N 1005
struct node
{
    double l,r;
}p[N];
double x[N],y[N];
bool cmp(node a,node b)
{
    return a.l<b.l;
}
int main()
{
    int i,n,d,cnt=1,flag;
    while(scanf("%d%d",&n,&d),n||d)
    {
        flag=0;
        for(i=0;i<n;i++)
        {
            scanf("%lf%lf",&x[i],&y[i]);
            if(flag)
                continue;
            if(d<y[i])
                flag=1;
            double t=sqrt(d*d-y[i]*y[i]);
            p[i].l=x[i]-t;
            p[i].r=x[i]+t;
        }
        printf("Case %d: ",cnt++);
        if(flag)
        {
            printf("-1\n");
            continue;
        }
        sort(p,p+n,cmp);
        int t=1;
        double rr;
        rr=p[0].r;
        for(i=1;i<n;i++)
        {
            if(p[i].l>rr)   //该区间不能被雷达覆盖住
            {
                rr=p[i].r;
                t++;
            }
            if(p[i].r<rr)  //可以被当前雷达作用，
            {
                rr=p[i].r;
            }
        }
        printf("%d\n",t);
    }
    return 0;
}

poj 1328 Radar Installation （贪心）

标签：des   style   http   color   os   io   strong   for   ar   

原文地址：http://blog.csdn.net/u011721440/article/details/38825649