input: Write a function to implement a sorting algorithm that takes two lists A and B. The algorithm should compare the first elements of both lists, adding the smaller element to the result list and moving the pointer to the next element. This process should continue until all elements from both lists are added to the result list in sorted order. If either list is exhausted, the remaining elements from the other list should be added directly to the result list. The function should return the merged sorted list.
  
  assert merge_sort([3, 6, 8, 10, 11], [2, 5, 7, 12]) == [2, 3, 5, 6, 7, 8, 10, 11, 12]
  assert merge_sort([1, 3, 5], [2, 4, 6]) == [1, 2, 3, 4, 5, 6]
  assert merge_sort([], [1, 2, 3]) == [1, 2, 3]
  assert merge_sort([1, 2, 3], []) == [1, 2, 3]
  assert merge_sort([], []) == []
output: def merge_sort(A, B):
      result = []
      i, j = 0, 0
      while i < len(A) and j < len(B):
          if A[i] < B[j]:
              result.append(A[i])
              i += 1
          else:
              result.append(B[j])
              j += 1
      result.extend(A[i:])
      result.extend(B[j:])
      return result