78. Subsets

设定列表path记录路过的值，使用loop和pointer确定subset开始的位置，dfs完之后pop最后一个值。

public static List<List<Integer>> subsets(int[] nums) {
    List<List<Integer>> res = new ArrayList<>();
    List<Integer> path = new ArrayList<>();
    dfs(nums, path, res, 0);
    return res;
}

public static void dfs(int[] nums, List<Integer> path, List<List<Integer>> res, int pointer) {
    res.add(new ArrayList<>(path));
    for (int i = pointer; i < nums.length; i++) {
        path.add(nums[i]);
        dfs(nums, path, res, i + 1);
        path.remove(path.size() - 1);
    }
}