Prefix Sum pattern
Count Vowels in Substrings
Given a string, precompute prefix counts of vowels so that the number of vowels in any substring range can be answered in constant time per query. Watch it run step by step, then write your own pseudocode and get it checked by AI.
- 2 approaches
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Prefix Sum
From the first idea to the best one
- 01 Brute force · scan each query O(n · q)O(1) space
- 02 Optimized · prefix vowel counts O(n + q)O(n) space
What you will learn
- How to read Count Vowels in Substrings and spot the prefix sum pattern in it
- Brute force · scan each query: O(n · q) time, O(1) space
- Optimized · prefix vowel counts: O(n + q) time, O(n) space
- The pseudocode for each approach, its line lit as the animation runs
- Practice: write your own pseudocode and get it checked
More Prefix Sum
See Count Vowels in Substrings run, step by step
Sign in and this page opens on the animation, with all 2 Prefix Sum problems beside it.
DSA comes with the all labs plan and every ChaiCode batch.