POJ-3069 Saruman's Army

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, …, x_n of each troop (where 0 ≤ x_i ≤ 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

---

 

#include <iostream>
#include <algorithm>
using namespace std;

int main(void)
{
    int r, n, i, p;
    int point[300];
    
    while(cin >> r >> n && r != -1 && n != -1)  {
        for(i = 0; i < n; i++)
            cin >> point[i];
        
        sort(point, point+n);
        
        i = 0;
        int ans = 0;
        while(i < n)    {
            int s = point[i++];          //s是没有被覆盖的最左边的点
            
            while(point[i] <= s+r && i < n)
                i++;
            
            p = point[i-1];         //p为被标记的点
            
            while(point[i] <= p+r && i < n)
                i++;
            
            ans++;
            
            
            
        }
        
        
        cout << ans << endl;
    }
    
    
    return 0;
}