POJ

Saruman's Army

Time Limit: 1000MS Memory Limit: 65536KTotal Submissions: 10942 Accepted: 5526

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

0 310 20 2010 770 30 1 7 15 20 50-1 -1

Sample Output

24

题意：有n个点，需要标记若干个点，让若干个点的左右r范围把所有的点都包括。

解决：贪心，排序后从前往后

#include <iostream>#include <algorithm>#include <cstdio>using namespace std;int r, n, x[1005];int main(){    while(cin >> r >> n && r != -1 && n != -1){        for(int i = 0; i < n; i++)            cin >> x[i];        sort(x, x+n);        int ans = 0;        int i = 0;        while(i < n){            int s = x[i++];            while(i < n && x[i] <= s + r) i++;            int p = x[i - 1];           // printf("%d---------\n", p);            while(i < n && x[i] <= p + r) i++;            ans++;        }        cout << ans << endl;    }}