78. 子集

class Solution {
    List<List<Integer>> res;
    List<Integer> path;
    int[] nums;
    public List<List<Integer>> subsets(int[] nums) {
        res = new ArrayList<>();
        path = new ArrayList<>();
        this.nums = nums;
        dfs(0);
        return res;
    }

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