class Solution:
    def nextPermutation(self, nums: List[int]) -> None:
        i = len(nums) - 2
        while i >= 0 and nums[i + 1] <= nums[i]:
            i -= 1
        if i >= 0:
            j = len(nums) - 1
            while nums[j] <= nums[i]:
                j -= 1
            self.swap(nums, i, j)
        self.reverse(nums, i + 1)
# (Helper methods continued on next slide)