78. 子集

套模板，可参考：https://www.cnblogs.com/panweiwei/p/14025143.html

class Solution(object):
    def __init__(self):
        self.res = []

    def subsets(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        if not nums:
            return []
        n = len(nums)
        self.dfs(nums, n, 0, [])
        return self.res

    def dfs(self, nums, n, begin, temp):
        self.res.append(temp)
        for i in range(begin, n):
            self.dfs(nums, n, i + 1, temp + [nums[i]])