impl Solution {
    fn dfs(nums: &Vec<i32>, i: usize, res: &mut Vec<Vec<i32>>, list: &mut Vec<i32>) {
        if i == nums.len() {
            res.push(list.clone());
            return;
        }
        list.push(nums[i]);
        Self::dfs(nums, i + 1, res, list);
        list.pop();
        Self::dfs(nums, i + 1, res, list);
    }

    pub fn subsets(nums: Vec<i32>) -> Vec<Vec<i32>> {
        let mut res = vec![];
        Self::dfs(&nums, 0, &mut res, &mut vec![]);
        res
    }
}