31.md

32ms beat: 99.06%

class Solution:
    def nextPermutation(self, nums: List[int]) -> None:
        """
        Do not return anything, modify nums in-place instead.
        """
        k = len(nums) - 2
        while k >=0 and nums[k] >= nums[k+1]:
            k -= 1
        if k < 0:
            self.reverse(nums, 0, len(nums)-1)
        else:
            l = len(nums) - 1
            while nums[l] <= nums[k]:
                l -= 1
            nums[k], nums[l] = nums[l], nums[k]
            self.reverse(nums, k + 1, len(nums)-1)
        
    def reverse(self, nums, left, right):
        while left < right:
            nums[left], nums[right] = nums[right], nums[left]
            left += 1
            right -= 1