```
def nextPermutation(self, nums):
i = j = len(nums)-1
while i > 0 and nums[i-1] >= nums[i]:
i -= 1
if i == 0: # nums are in descending order
nums.reverse()
return
k = i - 1 # find the last "ascending" position
while nums[j] <= nums[k]:
j -= 1
nums[k], nums[j] = nums[j], nums[k]
l, r = k+1, len(nums)-1 # reverse the second part
while l < r:
nums[l], nums[r] = nums[r], nums[l]
l +=1 ; r -= 1
```