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, …, 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.
题意:
给出几个点,给出半径,要求尽可能少标记几个点,实现对全部点的覆盖。
思路:
按照坐标排序,然后从左向右依次,第一个点是为标记的点找到最有段半径内的点,标记它,然后以标记点向右覆盖,找到第一个没有覆盖掉点,重复上述操作,知道结束。
#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++; ans++; } return ans; } int main() { ///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; }