main.py

class Solution:

    def merge(self, nums1: List[int], m: int, nums2: List[int], n: int) -> None:
        """
        Do not return anything, modify nums1 in-place instead.
        """
        i, j = m - 1, n - 1
        for p in reversed(range(m + n)):
            if i < 0:
                nums1[p] = nums2[j]
                j -= 1
            elif j < 0:
                nums1[p] = nums1[i]
                i -= 1
            elif nums1[i] > nums2[j]:
                nums1[p] = nums1[i]
                i -= 1
            else:
                nums1[p] = nums2[j]
                j -= 1


class Solution:

    def merge(self, nums1: List[int], m: int, nums2: List[int], n: int) -> None:
        """
        Do not return anything, modify nums1 in-place instead.
        """
        i = m - 1
        j = n - 1
        for p in reversed(range(m + n)):
            if i < 0:
                nums1[p] = nums2[j]
                j -= 1
            elif j < 0:
                break
            else:
                a = nums1[i]
                b = nums2[j]
                if a > b:
                    nums1[p] = a
                    i -= 1
                else:  # b >= a
                    nums1[p] = b
                    j -= 1