Most people think this is a “simple” problem.
Reverse an array.
But there are actually two very different ways to think about it
Approach 1: Let Python do the work
arr[::-1]
That’s it.
Looks clean. Works instantly.
But under the hood:
- In a Python list, this creates a new array
- It walks from end → start and copies elements
Time: O(n)
Space: O(n)
One interesting twist:
- In NumPy, slicing often gives a view, not a full copy
→ same code, very different memory behavior
Approach 2: Swap from both ends
left, right = 0, len(arr) - 1
while left < right:
arr[left], arr[right] = arr[right], arr[left]
left += 1
right -= 1
Here you’re not creating anything new.
Just swapping:
- first ↔ last
- then moving inward
Time: O(n)
Space: O(1)
What this really shows
Both solve the same problem.
But one is:
“just get it done”
The other is:
“do it with control”
And honestly, both are useful, depends on what you care about in that moment.
Small takeaway
Sometimes the difference in solutions isn’t about correctness.
It’s about:
- how much you understand
- and how much you care about what’s happening underneath
Next time something feels “too easy”…
there’s probably a deeper layer sitting right below it.
