[백준/BOJ] 15651. N과 M (3) [Silver 3]

15651. N과 M (3)
       문제출처 : https://www.acmicpc.net/problem/15651

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.StringTokenizer;

public class baekjoon15651 {
    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
    static StringTokenizer st;
    static int N,M;
    static int[] arr;

    public static void func(int index) throws IOException{
        if(index == M){
            for(int i=0;i<M;i++){
                bw.write(Integer.toString(arr[i])+" ");
            }
            bw.newLine();
            return;
        }
        for(int i=0;i<N;i++){
            arr[index]=i+1;
            func(index+1);
        }
    }
    public static void main(String args[]) throws IOException{
        st = new StringTokenizer(br.readLine());
        N = Integer.parseInt(st.nextToken());
        M = Integer.parseInt(st.nextToken());

        arr = new int[M];
        func(0);
        bw.flush();
        bw.close();
    }
}

아무리 재귀함수를 공부해도 어려워서 차근차근 다시해나가고 있다.
dfs랑 백트래킹이랑 뭔차인가했더니
dfs기 백트래킹 방법중 한개였다...