How do you find the longest common prefix among an array of strings?
PICTURE THIS: ARRAY IN MEMORY
Index starts at 0. Scan once for max — O(n).
Simple meaning
Take the first string as a candidate and shrink it whenever a later string mismatches at some index.
WHY — Strings instead of guessing?
Why interviewers care about Strings:
question about Strings.
trade-offs, and what you would actually do on a DSA project - not buzzwords.
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:
- 1Take the first string
as a candidate and shrink it whenever a later string mismatches at some index.
- 2Worst-case time is O(total
characters) and extra space is O(1) besides the prefix.
- 3Horizontal scanning, vertical scanning,
and a trie all work
- 4vertical scan can exit
early on the first mismatch column.
- 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
Take the first string as a candidate and shrink it whenever a later string mismatches at some index. Worst-case time is O(total characters) and extra space is O(1) besides the prefix.