combinationのeclipse実行結果
6057 ワード
1 import java.util.ArrayList;
2 import java.util.Arrays;
3
4
5 public class Combination {
6
7 public static ArrayList<ArrayList<Integer>> combine(int n, int k) {
8 ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
9 if(n <= 0||n < k)
10 return res;
11 ArrayList<Integer> item = new ArrayList<Integer>();
12 dfs(n,k,1,item, res);//because it need to begin from 1
13 return res;
14 }
15
16 private static void dfs(int n, int k, int start, ArrayList<Integer> item, ArrayList<ArrayList<Integer>> res){
17 if(item.size()==k){
18 res.add(new ArrayList<Integer>(item));//because item is ArrayList<T> so it will not disappear from stack to stack
19 System.out.println(item);
20 return;
21 }
22 for(int i=start;i<=n;i++){
23 System.out.println(i);
24 item.add(i);
25 dfs(n,k,i+1,item,res);
26 System.out.println(i);
27 item.remove(item.size()-1);
28 System.out.println(item);
29
30 }
31 }
32
33 public static void main(String[] args)
34 {
35 ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
36 res=combine(3,2);
37 System.out.println(res);
38
39 }
40
41 }1
2
[1, 2]
2
[1]
3
[1, 3]
3
[1]
1
[]
2
3
[2, 3]
3
[2]
2
[]
3
3
[]
[[1, 2], [1, 3], [2, 3]]