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(No loops needed)
An algorithm is O(1) if it takes the same time regardless of input size. Array access is O(1). Hash table lookups are O(1). Adding two numbers is O(1).
This does not mean instant. It means the time does not depend on n. Reading arr[0] and arr[999] both take one step.
If you can solve a problem without scanning the input, you usually get O(1).
