package question;

import java.util.LinkedList;
import java.util.List;

public class Question77 {
 public static void main(String[] args) {
 new Question77().combine(4, 2).forEach(System.out::println);
 }

 List<List<Integer>> res = new LinkedList<>();

 public List<List<Integer>> combine(int n, int k) {
 if (n == 0 || k == 0) return res;
 for (int i = 1; i <= n; i++) {
 List<Integer> list = new LinkedList<>();
 list.add(i);
 huiSu(list, k, n);
 }
 return res;
 }

 public void huiSu(List<Integer> list, int k, int n) {
 if (list.size() == k) {
 res.add(new LinkedList<>(list));
 return;
 }
 for (int i = list.get(list.size() - 1) + 1; i <= n; i++) {
 list.add(i);
 huiSu(list, k, n);
 list.remove(list.size() - 1);
 }
 }
}