给定一个数组，找出数组中不曾出现的最小正整数。
关键在于需要对原数组进行操作。
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