def merge(self, nums1, m, nums2, n):
    """
    :type nums1: List[int]
    :type m: int
    :type nums2: List[int]
    :type n: int
    :rtype: None Do not return anything, modify nums1 in-place instead.
    """
    idxM = m - 1                        # the end index of nums1
    idxN = n - 1                        # the end index of nums2
    destination = m + n - 1             # we will write to nums1 from the end
    while destination >= 0:
        if idxM < 0:                            # if we only have nums2, copy those
            nums1[destination] = nums2[idxN]
            idxN -= 1
        elif idxN < 0:                          # else if we only have nums1, copy those
            nums1[destination] = nums1[idxM]
            idxM -= 1
        elif nums2[idxN] > nums1[idxM]:         # if num2 greater, write it at destination
            nums1[destination] = nums2[idxN]
            idxN -= 1
        else:
            # else num1 is greater, write it at destination and overwrite the existing location with min
            nums1[destination], nums1[idxM] = nums1[idxM], -maxint-1
            idxM -= 1
        destination -= 1