What is the time complexity of accessing an array index?
PICTURE THIS: ARRAY IN MEMORY
Index starts at 0. Scan once for max — O(n).
Simple meaning
Access by index is O(1) because the address is base plus index times size.
WHY — Arrays instead of guessing?
Why interviewers care about Arrays:
who only read docs from people who shipped.
and tied to DSA work.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1Access by index is
O(1) because the address is base plus index times size.
- 2Searching an unsorted array
without an index map is O(n).
- 3I separate access from
search in interviews.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
Access by index is O(1) because the address is base plus index times size. Searching an unsorted array without an index map is O(n).