lintcode 中等题：subsets II 带重复元素的子集

class Solution:
    """
    @param S: A set of numbers.
    @return: A list of lists. All valid subsets.
    """
    def subsetsWithDup(self, nums):
        # write your code here
        res = []
        size = len(nums)
        nums.sort()
        if nums == None or size == 0:
            return res
        for i in range(1<<size):
            lst=[]
            n = i
            for j in range(size):
                if n%2==1:
                    lst.append(nums[j])
                n/=2
            if lst not in res:
                res.append(lst)
        return res