What is the time complexity level of adding an element to the end of an array using a slice?

In Go, the operation of adding an element to the end of a slice (append) has an amortized time complexity of O(1).

Explanation:

• If the slice has enough allocated capacity (capacity), then adding an element is simply a matter of writing to the next free index — this operation takes constant time.

• If the capacity is insufficient, a new larger array is allocated, old elements are copied, and the new element is added — this operation takes O(n), where n is the current size of the slice.

However, since such reallocations do not occur with every addition but only periodically, the average (amortized) complexity of adding remains O(1).