백준 N과M(9)

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.StringTokenizer;
 
public class Main{
    private static int[] arr;
    private static LinkedHashSet<String> hs;
 
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer(br.readLine(), " ");
        StringBuilder sb = new StringBuilder();
        int N = Integer.parseInt(st.nextToken());
        int M = Integer.parseInt(st.nextToken());
        hs = new LinkedHashSet<String>();
        
        arr = new int[N];
        int[] a = new int[N]; // 인덱스를 관리하는 배열
        st = new StringTokenizer(br.readLine(), " ");
        for (int i = 0; i < arr.length; i++) {
            arr[i] = Integer.parseInt(st.nextToken());
        }
        Arrays.sort(arr);
        backtrack(a, 0, M);
          for(String s : hs) {
                sb.append(s.substring(0, s.length()-1)).append("\n");
            }
            System.out.print(sb.toString());
    }
 
    public static void backtrack(int[] a, int k, int r) {
        int[] c = new int[a.length]; // 후보군을 담는 배열
        if (k == r) {
            print(a, k);
 
        } else {
            int cands = make_candidates(a, k, r, c);
            for (int i = 0; i < cands; i++) {
                a[k] = c[i];
                backtrack(a, k + 1, r);
            }
        }
 
    }
 
    public static int make_candidates(int[] a, int k, int r, int[] c) {
        boolean[] flag = new boolean[a.length];
        for (int i = 0; i < k; i++) {
 
            flag[a[i]] = true;
 
        }
 
        int cnt = 0;
        for (int i = 0; i < flag.length; i++) {
            if (!flag[i]) {
                c[cnt] = i;
                cnt++;
            }
        }
        return cnt;
    }
 
    public static void print(int[] a, int r) {
        String s = "";
        for (int i = 0; i < r; i++) {
            s=s + arr[a[i]] + " ";
        }
            hs.add(s);
 
    }
 
}
 

중복때문에 LinkedHashSet 사용 순서 허용 O 중복 허용 X