boj_15652.java

package backtracking;

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

public class boj_15652 {
    static int N,M;
    static int[] arr;
    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);
    }

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

        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);
        }
    }

}