How do you compute the next permutation of an array of numbers?
PICTURE THIS: ARRAY IN MEMORY
Index starts at 0. Scan once for max — O(n).
Simple meaning
Find the rightmost ascent, swap it with the smallest larger successor on its right, then reverse the suffix to make it the next smallest order.
WHY — Arrays instead of guessing?
Why interviewers care about Arrays:
question about Arrays.
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:
- 1Find the rightmost ascent,
swap it with the smallest larger successor on its right, then reverse the suffix to make it the next smallest order.
- 2The walk is O(n)
time and O(1) extra space.
- 3If the array is
strictly decreasing it is the last permutation, so reverse the whole array to the first.
- 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
Find the rightmost ascent, swap it with the smallest larger successor on its right, then reverse the suffix to make it the next smallest order. The walk is O(n) time and O(1) extra space.