Count Vowels Permutation || Leetcode Hard 1220 || Dynamic Programming

Опубликовано: 18 Апрель 2026
на канале: Digital Interview
141
3

Given an integer n, your task is to count how many strings of length n can be formed under the following rules:

Each character is a lower case vowel ('a', 'e', 'i', 'o', 'u')
Each vowel 'a' may only be followed by an 'e'.
Each vowel 'e' may only be followed by an 'a' or an 'i'.
Each vowel 'i' may not be followed by another 'i'.
Each vowel 'o' may only be followed by an 'i' or a 'u'.
Each vowel 'u' may only be followed by an 'a'.
Since the answer may be too large, return it modulo 10^9 + 7.



Example 1:

Input: n = 1
Output: 5
Explanation: All possible strings are: "a", "e", "i" , "o" and "u".

Get notified about all off campus jobs/interviews and the process.
We are building our website and it will be back soon with lots of content till then subscribe us on youTube.
https://t.me/tech_geek1

Interview Preparation Sheet:    • INTERVIEW PREPARATION SHEET - HASHEDIN and...  

Link for Leetcode solutions:    • Leetcode Solutions  

Link for placement series:
Placement 2022:    • Placements 2022  
Placement 2023:    • Placements 2023  

#leetcode #leetcodesolution