活动选择问题

import java.util.*;

//Simple pair class to store the start time and finish time
//of the activities
class Pair
{
 private int start, finish;

 public Pair(int start, int finish) {
     this.start = start;
     this.finish = finish;
 }

 public int getFinish() {
     return finish;
 }

 public int getStart() {
     return start;
 }

 public String toString() {
     return "(" + getStart() + " " + getFinish() + ")";
 }
};

public class A080
{
 public static Set<Integer> selectActivity(List<Pair> activities)
 {
     int k = 0;
     Set<Integer> out = new HashSet<>();

     out.add(0);
     for (int i = 1; i < activities.size(); i++)
     {
         if (activities.get(i).getStart() >= activities.get(k).getFinish())
         {
             out.add(i);
             k = i;    
         }
     }

     return out;
 }

 public static void main(String[] args)
 {
     List<Pair> activities = Arrays.asList(new Pair(1, 4), new Pair(3, 5),
             new Pair(0, 6), new Pair(5, 7), new Pair(3, 8),
             new Pair(5, 9), new Pair(6, 10), new Pair(8, 11),
             new Pair(8, 12), new Pair(2, 13), new Pair(12, 14));

     Collections.sort(activities, (a, b) -> a.getFinish() - b.getFinish());

     Set<Integer> res = selectActivity(activities);

     for (Integer i: res) {
         System.out.print(activities.get(i));
     }
 }
}