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1641. Count Sorted Vowel Strings

Difficulty Topics

Description

Given an integer n, return the number of strings of length n that consist only of vowels (a, e, i, o, u) and are lexicographically sorted.

A string s is lexicographically sorted if for all valid i, s[i] is the same as or comes before s[i+1] in the alphabet.

 

Example 1:

Input: n = 1
Output: 5
Explanation: The 5 sorted strings that consist of vowels only are ["a","e","i","o","u"].

Example 2:

Input: n = 2
Output: 15
Explanation: The 15 sorted strings that consist of vowels only are
["aa","ae","ai","ao","au","ee","ei","eo","eu","ii","io","iu","oo","ou","uu"].
Note that "ea" is not a valid string since 'e' comes after 'a' in the alphabet.

Example 3:

Input: n = 33
Output: 66045

 

Constraints:

  • 1 <= n <= 50 

Solution

count-sorted-vowel-strings.py
class Solution:
    def countVowelStrings(self, n: int) -> int:
        a = e = i = o = u = 1

        for _ in range(n - 1):
            a, e, i, o, u = a + e + i + o + u, e + i + o + u, i + o + u, o + u, u

        return a + e + i + o + u