算法入门 6.Saruman‘s Army（贪心）

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

#include<iostream>
using namespace std;
int n,r;
const int maxn=1e7;
int a[maxn];
int sum;
void init(){
    cin>>n>>r;
    for(int i=0;i<n;i++) cin>>a[i];
}
void solve(){
    sort(a,a+n);
    int i=0;
    sum=0;
    while(i<n){
        int s=a[i++];
        while(i<r&&a[i]<=s+r) i++;
        int p=a[i-1];
        while(i<n&&a[i]<=r+p) i++;
        sum++;
    }
    cout<<sum<<endl;
}
int main(){
    init();
    solve();
}