选择物品

终于有一道我能做的题了，，，

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.util.ArrayList;
public class Main {
    public static ArrayList> res = new ArrayList();
    public static ArrayList path = new ArrayList();
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] params = br.readLine().trim().split(" ");
        int n = Integer.parseInt(params[0]), m = Integer.parseInt(params[1]);
        dfs(n, m, 1);
        for(ArrayList items: res){
            for(Integer elem : items){
                System.out.print(elem + " ");
            }
            System.out.println();
        }
    }
    private static void dfs(int n, int m, int index) {
        if(path.size() == m){
            res.add(new ArrayList(path));
            return;
        }
        for(int i = index; i <= n; i++){
            path.add(i);
            dfs(n, m, i + 1);
            path.remove(path.size() - 1);
        }
    }
}