Rotate Array
mediumTime: O(n)Space: O(1)
Signals to notice
rotate array by k positionsin-placecyclic shift
Brute force first
Shift elements one by one, k times. It is a fair place to begin because it matches the surface of the question, yet it does not capture the deeper structure that makes the problem simpler.
The key insight
Reverse entire array, reverse first k, reverse rest. The goal is not to be clever for its own sake, but to remember the one relationship that keeps the solution grounded as you move forward.
What must stay true
Three reverses achieve a rotation: reverse all, reverse [0.k-1], reverse [k.n-1]. If that remains true after every update, the rest of the reasoning has a stable place to stand.
Easy way to go wrong
Not handling k > n — use k = k % n first. Most mistakes here are not about syntax; they come from losing track of what your state, pointer, or structure is supposed to mean.