[JAVA] 순열, 조합, 부분집합

까먹기 싫어서 쓰는 순열, 조합
어려워서 외웁니다.

import java.io.*;
import java.util.*;

public class Main {
    static int n, r;
    static boolean[] visit;
    static int[] operations, per_array, com_array;

    public static void main(String[] args) throws IOException {
    	BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
    	n = Integer.parseInt(bf.readLine());
    	r = Integer.parseInt(bf.readLine());
        operations = new int[] {1, 2, 3, 4, 5, 6};
        visit = new boolean[n];
        per_array = new int[r];
        com_array = new int[r];
        
        System.out.println("---------순열----------");
        per(0);
        System.out.println("---------조합----------");
        com(0, 0);
        System.out.println("---------부분집합----------");
        subset();
        
    }

    public static void per(int depth) {
        if (r == depth) {
            System.out.println(java.util.Arrays.toString(per_array));
            return;
        }

        for (int i = 0; i < n; i++) {
            if (!visit[i]) {
                visit[i] = true;
                per_array[depth] = operations[i];
                per(depth + 1);
                visit[i] = false;
            }
        }
    }
    
    public static void com(int start, int depth) {
    	if (r==depth) {
    		System.out.println(java.util.Arrays.toString(com_array));
    		return;
    	}
    	for(int i=start; i < n; i++) {
    		com_array[depth] = operations[i];
    		com(i+1,depth+1);
    	}
    	
    }
    
    public static void 	subset() {
		for(int i=0; i<(1<<n); i++) {
			Set<Integer> set = new HashSet<>();
			for(int j=0; j<n; j++) {
				if((i &(1<<j)) != 0) {
					set.add(operations[j]);
				}
			}
			System.out.println(set);
		}
	}
}