Leetcode_Python 41 缺失的第一个正数

class Solution(object):
    def firstMissingPositive(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        nums = list(set(nums))
        if nums == []:
            return 1
        for i,num in enumerate(nums):
            if num < 0 or num> len(nums):
                nums[i] = 0
        for i in range(len(nums)):
            while (nums[i] != i+1) and (nums[i] > 0):  #如果      
                a = nums[nums[i]-1]
                nums[nums[i]-1] = nums[i]# 
                nums[i] = a
        for i,num in enumerate(nums):
            if num == 0:
                return i+1
            elif i == len(nums)-1:
                return num+1
a = Solution()
a.firstMissingPositive([])