input: def merge_sort(A, B):
      """ Implement an algorithm to sort two large lists A and B. The algorithm should take the first element of list A and compare it with the first element of list B. If it is greater, then it should add the element to the result list and move the pointer of B to the next element. If the element of A is smaller, the pointer should move to the next element of A, and so on.
      >>> merge_sort([3, 6, 8, 10, 11], [2, 5, 7, 12])
      [2, 3, 5, 6, 7, 8, 10, 11, 12]
      """
output:     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