class Solution:
def firstMissingPositive(self, nums: List[int]) -> int:
if not nums or len(nums)==0:return 1
i=0
while i <len(nums):
if nums[i]==i+1:
i+=1
elif nums[i]<=len(nums) and nums[i]>0:
tmp=nums[nums[i]-1]
if tmp==nums[i]:
i+=1
continue
nums[nums[i]-1]=nums[i]
nums[i]=tmp
else:
i+=1
for i in range(len(nums)):
if nums[i]!=i+1:
return i+1
return len(nums)+1
