import java.util.*; public class Solution { ArrayList<ArrayList<Integer>> res = new ArrayList<>(); ArrayList<Integer> track = new ArrayList<>(); public ArrayList<ArrayList<Integer>> subsets(int[] S) { backtrack(0,S); return res; } private void backtrack(int start,int[] s){ res.add(new ArrayList<>(track)); for(int i = start; i < s.length;i++){ track.add(s[i]); backtrack(i + 1,s); track.remove(track.size()-1); } } }