백준 N과M(3)

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.StringTokenizer;
public class Main{
	private static int[] arr;
	private static StringBuilder sb;
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer(br.readLine(), " ");
		int N = Integer.parseInt(st.nextToken());
		int M = Integer.parseInt(st.nextToken());
		sb = new StringBuilder();
		arr = new int[N];
		int[] a = new int[N]; // 인덱스를 관리하는 배열
		for (int i = 0; i < N; i++) {
			arr[i] = i + 1;
		}
		int depth = 0;
		backtrack(a, depth ,M);
		System.out.println(sb);
	}
	
	public static void backtrack(int[] a, int depth, int M) {
		if(depth == M ) {
			for (int j = 0; j < M; j++) {
						sb.append(arr[a[j]]).append(" ");
			}
			sb.append("\n");
			return;
		}
		
		for (int i = 0; i < a.length; i++) {
			a[depth] = i;
			backtrack(a, depth+1, M);
		}
	}
}