POJ3069 Saruman's Army【贪心】

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, …, xnof 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

思路：从最左边开始，找r范围内最右边的点，然后在超出r范围的最左边点当做起始点继续寻找。

#include<iostream>
#include<cstdio>
#include<string>
#include<cstring>
#include<algorithm>
using namespace std;       
const int maxn=1005;
int main()   
{
    int n,r, arr[maxn];
    while(scanf("%d%d",&r,&n)!=EOF && n+r!=-2)
    {
        for(int i=0;i<n;++i)
            scanf("%d",&arr[i]);
        sort(arr,arr+n);
        int i=0,ans=0;
        while(i<n)
        {
            int s=arr[i++];
            while(i<n && arr[i]<=s+r)
                ++i;
            int p=arr[i-1];
            while(i<n && arr[i]<=p+r)
                ++i;
            ++ans;
        }
        printf("%d\n",ans);
    }
    return 0;
}