How should I practice Count Vowel Permutations?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Zscaler onsite interview problems in FastPrep.

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Count Vowel Permutations

Zscaler● MediumINTERNONSITE INTERVIEW

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Problem statement

Return the number of length-n strings made only from a, e, i, o, and u that follow these rules:

a may be followed only by e.
e may be followed only by a or i.
i may be followed by a, e, o, or u.
o may be followed only by i or u.
u may be followed only by a.

Return the count modulo 1,000,000,007.

Function

countVowelPermutations(n: int) → int

Examples

Example 1

n = 1return = 5

Every single vowel is valid.

Example 2

n = 2return = 10

The valid transitions are ae, ea, ei, ia, ie, io, iu, oi, ou, ua.

Example 3

n = 5return = 68

Dynamic programming counts valid strings ending in each vowel after five positions.

Constraints

1 <= n <= 20000