Rotation & Rearrangement

You’re listening to your playlist:

[Song A, Song B, Song C, Song D, Song E]

But today you want a different vibe.

Instead of creating a new playlist, you simply say:

“Move the last 2 songs to the front.”

Now it becomes:

[Song D, Song E, Song A, Song B, Song C]

You didn’t change the songs.
You just changed their positions.

That’s exactly what rotation and rearrangement problems are.

Array Rotation (Shift the Perspective)

Concept - Rotate Array by K Steps

Rotate right by k

def rotate(arr, k):

k = k % len(arr)

return arr[-k:] + arr[:-k]

Technical Example:

Input:  [1, 2, 3, 4, 5], k = 2

Output: [4, 5, 1, 2, 3]

Real-Life Insight:

• Rotating shifts in a weekly schedule
• Moving last tasks to the beginning

In-Place Rotation (Interview Favorite)

Interviewers often ask:

“Can you do it without extra space?”

Trick: Reverse Method

Code Example:

???? Time = O(n), Space = O(1)

Rearrangement (Changing Pattern)

Move All Zeros to End

Example:

Input:  [0,1,0,3,12]

Output: [1,3,12,0,0]

Real-Life Example:

Pushing all inactive tasks to the end of a list.

Rearranging Positive & Negative Numbers

Alternate Arrangement

Arrange positives and negatives alternately

Key Patterns to Recognize

Interviewers may not say “rotation” directly.

They say:

• “Shift elements”
• “Reorder array”
• “Cyclic movement”
• “In-place modification”

All hint toward rotation/rearrangement

Rotation doesn’t change data
it changes how you look at the data.

• Rotation = Circular shift
• Rearrangement = Pattern change
• Optimization = Do it in-place