Problem can be found in here!
def merge(nums1: List[int], m: int, nums2: List[int], n: int) -> None:
i, j = m-1, n-1
index = m + n - 1
while j >= 0:
if i >= 0 and nums1[i] >= nums2[j]:
nums1[index] = nums1[i]
i -= 1
else:
nums1[index] = nums2[j]
j -= 1
index -= 1