How to determine the time complexity of accessing an element by key in a Map data structure?

In a Map data structure (for example, in JavaScript or Java), access to an element by key usually has a time complexity of O(1) — that is, constant time. This is achieved by using hash tables, where the key is converted into an array index via a hash function.

However, in the worst case (for example, with a large number of collisions), the complexity can degrade to O(n), where n is the number of elements in the Map.

In summary:

• Average time complexity for key access: O(1)
• Worst-case time complexity: O(n) (rare, during collisions)