Watch 10 video solutions for Count Vowels Permutation, a hard level problem involving Dynamic Programming. This walkthrough by NeetCode has 44,927 views views. Want to try solving it yourself? Practice on FleetCode or read the detailed text solution.
Given an integer n, your task is to count how many strings of length n can be formed under the following rules:
'a', 'e', 'i', 'o', 'u')'a' may only be followed by an 'e'.'e' may only be followed by an 'a' or an 'i'.'i' may not be followed by another 'i'.'o' may only be followed by an 'i' or a 'u'.'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".
Example 2:
Input: n = 2 Output: 10 Explanation: All possible strings are: "ae", "ea", "ei", "ia", "ie", "io", "iu", "oi", "ou" and "ua".
Example 3:
Input: n = 5 Output: 68
Constraints:
1 <= n <= 2 * 10^4