Sorted the list to make it more simple. Let me know if you have any questions.

```
class Solution(object):
def missingNumber(self, nums):
v = 0
nums = sorted(nums)
if nums[0] == 1: return 0
for i in range(0,len(nums)-1):
if not nums[i+1]:
return nums[i]+1
if nums[i]+1 != nums[i+1]:
return nums[i]+1
else:
v = nums[i]+1
return v + 1
```