Description
Saruman the White must lead his army along a straight path from Isengard to Helm’s Deep. To keep track of his forces, Saruman distributes seeing stones, known as palantirs, among the troops. Each palantir has a maximum effective range of R units, and must be carried by some troop in the army (i.e., palantirs are not allowed to “free float” in mid-air). Help Saruman take control of Middle Earth by determining the minimum number of palantirs needed for Saruman to ensure that each of his minions is within R units of some palantir.
Input
The input test file will contain multiple cases. Each test case begins with a single line containing an integer R, the maximum effective range of all palantirs (where 0 ≤ R ≤ 1000), and an integer n, the number of troops in Saruman’s army (where 1 ≤ n ≤ 1000). The next line contains n integers, indicating the positions x1, …, xn of each troop (where 0 ≤ xi ≤ 1000). The end-of-file is marked by a test case with R = n = −1.
Output
For each test case, print a single integer indicating the minimum number of palantirs needed.
Sample Input
0 3
10 20 20
10 7
70 30 1 7 15 20 50
-1 -1
Sample Output
2
4
题意:
直线上有N个点, 从这几个点中选取几个点加上标记, 对每个点, 其距离为R以内的区域里必须有带有标记的点。 请问至少有多少点被加上标记。
思路:
应该从最左边的s点开始搜寻距离s最远的小于r的点, 然后给它加上标记, 然后记下他的坐标d, 继续搜寻距离它r外最近的那个点, 以此类推。
代码如下:
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
using namespace std;
const int maxn=1005;
int a[maxn];
int r,n;
int main()
{
while(scanf("%d%d",&r,&n)!=EOF&&(r!=-1||n!=-1))
{
int num=0;
for (int i=0;i<n;i++)
scanf("%d",&a[i]);
sort(a,a+n);
int i=0;
while (i<n)
{
int s=a[i++];
while (i<n&&a[i]<=s+r)
i++;
num++;
int d=a[i-1];
while (i<n&&a[i]<=d+r)
i++;
}
printf("%d\n",num);
}
return 0;
}