조합 (DFS)

class Main {

	static int m, n;
	
	public void DFS (int level, int start, int []combi) {
		if( level == m) {
			for ( int x : combi)
				System.out.print(x+ " ");
			System.out.println();
		} else {
			for( int i=start; i <= n ; i++) {
				combi[level] = i;
				DFS(level+1, i +1, combi );
			}
			
		}
	}

	public static void main(String args[]) throws Exception {
		Main M = new Main();
		Scanner in = new Scanner(System.in);
		n = in.nextInt();
		m = in.nextInt();
		int []combi = new int[m];
		M.DFS(0, 1, combi);

	}

}
ex)
input
4 2
output
1 2
1 3
1 4
2 3
2 4
3 4