[백준 15652] N과 M (4)

import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.StringTokenizer;
import java.lang.StringBuilder;

public class Main {

    public static int N, M;
    public static int[] arr;

    public static StringBuilder sb = new StringBuilder();

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        StringTokenizer st = new StringTokenizer(br.readLine());

        N = Integer.parseInt(st.nextToken());
        M = Integer.parseInt(st.nextToken());
        arr = new int[M];

        dfs(1, 0);

        System.out.println(sb);
    }

    public static void dfs(int at, int depth) {

        // N개 만큼 순열 만드는게 끝났다면 출력
        if(depth == M) {
            for(int val : arr) {
                sb.append(val).append(' ');
            }

            sb.append('\n');

            return;
        }

        for(int i=at; i<=N; i++) {
            arr[depth] = i;
            dfs(i, depth + 1);
        }
    }
}