leetcode: 78. Subsets

# Given a set of distinct integers, nums, return all possible subsets (the power set).
#
# Note: The solution set must not contain duplicate subsets.
#
# For example,
# If nums = [1,2,3], a solution is:
#
# [
#   [3],
#   [1],
#   [2],
#   [1,2,3],
#   [1,3],
#   [2,3],
#   [1,2],
#   []
# ]

1. 每次对现有子集做一份 拷贝；
2. 从x中选定一个数，后插入 该拷贝中的所有样本 尾部；
3. 将拷贝集 并入 原子集。

class Solution():
    def subsets(self, x):
        if not x:
            return [[]]
        else:
            tmp = self.subsets(x[:-1])
            res = tmp + [i+[x[-1]] for i in tmp]
            return res


if __name__ == "__main__":
    assert Solution().subsets([1, 2, 3]) == [[], [1], [2], [1, 2], [3], [1, 3], [2, 3], [1, 2, 3]]

class Solution():
    def subsets(self, x):
        res = [[]]
        for i in range(len(x)):
            for j in range(len(res)):
                res.append(res[j]+[x[i]])
        return res



if __name__ == "__main__":
    assert Solution().subsets([1, 2, 3]) == [[], [1], [2], [1, 2], [3], [1, 3], [2, 3], [1, 2, 3]]