78. 子集

res = []
path = []

def backtrack(未探索区域, res, path):
    if path 满足条件:
        res.add(path) # 深度拷贝
        # return  # 如果不用继续搜索需要 return
    for 选择 in 未探索区域当前可能的选择:
        if 当前选择符合要求:
            path.add(当前选择)
            backtrack(新的未探索区域, res, path)
            path.pop()

class Solution:
    def subsets(self, nums: List[int]) -> List[List[int]]:
        def dfs(nums, i, res, path):
            res.append(copy.deepcopy(path))
            while i < len(nums):
                path.append(nums[i])
                dfs(nums, i + 1, res, path)
                path.pop()
                i += 1
        res, path = [], []
        dfs(nums, 0, res, path)
        return res

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

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