POJ3069 Saruman's Army

Saruman's Army Time Limit: 1000MS Memory Limit: 65536KTotal Submissions: 11250 Accepted: 5689

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

简单贪心题，从最左边的点开始，距离为R以内最远的点，选定了以后，再向右延伸，到达能覆盖的最远的点。再进行下一次标记。

#include <iostream> #include <cstdio> #include <cstdlib> #include <algorithm> #include <vector> #include <cmath> #include <cstring> #include <string> #define N 1e5+10 /* run this program using the console pauser or add your own getch, system("pause") or input loop */ using namespace std; int main(int argc, char** argv) { int r,n; while(~scanf("%d%d",&r,&n)) { int loc[1010]={0}; if(n==-1&&r==-1)break; for(int i=0;i<n;i++) scanf("%d",&loc[i]); sort(loc,loc+n); int index=0,cnt=0; while(index<n) { int s=loc[index]; while(loc[index]-s<=r) index++;//选定要标记的点 s=loc[index-1]; while(s+r>=loc[index-1]) index++;//向右延伸 index--; cnt++; } printf("%d\n",cnt); } return 0; }