single 3069

http://poj.org/problem?id=3069

 

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.

 

Title:

Given a few points and a radius, it is required to mark as few points as possible to achieve coverage of all points.

Ideas:

Sort by coordinates, then from left to right, the first point is to find the point within the radius of the most segment for the marked point, mark it, then cover it with the marked point to the right, find the first point that is not covered, repeat The above operation, know the end.

#include<iostream>
#include<algorithm>
using namespace std;
int r,n;
int a[1003];
int solve(){
    sort(a,a+n);
    int i = 0;
    int ans = 0;
    while(i < n){
        int s = a[i++];
        while(i < n && a[i] <= s + r) i++;
        int troop = a[i-1];
        while(i < n && a[i] <= troop + r) i++;
        years ++ ;
    }
    return ans;
}
intmain ()
{
    ///input
    while(cin >> r >> n && (r != -1) && (n != -1)){
        for(int i = 0 ; i < n;i++)
            cin >> a[i];
         ///solve
        int ans = solve();
        ///output
        cout << ans << endl;
    }

    return 0;
}

View Code