Maximum Number of Vowels in a Substring of Given Length
mediumTime: O(n)Space: O(1)
Recognize the pattern
max vowels in any substring of length kfixed-size windowcount vowels entering/leaving
Brute force idea
For each window count vowels — O(nk).
Better approach
Sliding window: maintain vowel count. +1 if entering char is vowel, -1 if leaving char is vowel. Track max. O(n).
Key invariant
Vowel count updates in O(1) per slide. Never recount the whole window.
Watch out for
Recounting each window — update incrementally.