DFS_78. 子集

输入: nums = [1,2,3]
输出:
[
[3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

class Solution {
    public List<List<Integer>> subsets(int[] nums) {
        List<List<Integer>> res = new LinkedList<>();
        if (nums.length == 0){
            return res;
        }
        Deque<Integer> path = new ArrayDeque<Integer>();
        int len = nums.length;
        for (int size = 0; size <= nums.length; size++) {
            dfs(0,nums, path, res, size); // 不同的子集大小
        }
        return res;
    }

    private void dfs(int first,int[] nums, Deque<Integer> path, List<List<Integer>> res,int size) {
        if (path.size() == size) {
            res.add(new ArrayList<>(path));
            return;
        }

        for (int i = first; i < nums.length; i++) {
            path.add(nums[i]);
            dfs(i + 1,nums,path,res,size);
            path.remove(nums[i]);
        }
    }
}