給定一個數組，找出數組中不曾出現的最小正整數。

關鍵在於需要對原數組進行操作。

class Solution:
    def firstMissingPositive(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        if not nums: return 1
        for i in range(len(nums)):
            while 0 < nums[i] <
 
 len(nums) and nums[nums[i] - 1] != nums[i]:
                temp = nums[i]
                nums[i] = nums[temp - 1]
                nums[temp - 1] = temp
        print(nums)
        for i in range(len(nums)):
            if nums[i] != i + 1:
                return i + 1
        return len(nums)+1

leetcode41. First Missing Positive