When considering the efficiency of insertion and deletion operations, what is the primary difference between an array-based list and a linked list?

The primary difference between an array-based list and a linked list when considering the efficiency of insertion and deletion operations lies in how these operations are performed in each data structure.

1. Array-based list: In an array-based list, elements are stored in contiguous memory locations. When an element is inserted or deleted, the elements after it need to be shifted to maintain this contiguous nature. This results in a time complexity of O(n) for both insertion and deletion operations, where n is the number of elements in the list. This is because, in the worst-case scenario, you may need to shift all the elements.

2. Linked list: In a linked list, elements are stored in nodes, and each node has a reference to the next node in the list. Insertion or deletion of a node only involves changing the reference of the previous and next nodes, which can be done in constant time, O(1). However, if you need to insert or delete a node at a specific position, you would first need to traverse the list to find that position, which takes O(n) time.

So, the primary difference is that array-based lists take O(n) time for insertion and deletion in any case, while linked lists can perform these operations in O(1) time if the position is known, but finding a specific position takes O(n) time.