Solution.java

class Solution {
    private List<List<Integer>> ans = new ArrayList<>();
    private List<Integer> t = new ArrayList<>();
    private int[] nums;

    public List<List<Integer>> subsets(int[] nums) {
        this.nums = nums;
        dfs(0);
        return ans;
    }

    private void dfs(int i) {
        if (i == nums.length) {
            ans.add(new ArrayList<>(t));
            return;
        }
        dfs(i + 1);
        t.add(nums[i]);
        dfs(i + 1);
        t.remove(t.size() - 1);
    }
}