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Problem · Dynamic Programming

Strings With No k Consecutive Identical Characters

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Problem statement

You are given two integers:

n: length of string
k: maximum allowed consecutive identical characters

A string is invalid if it contains k or more consecutive identical characters.

Return the total number of strings of length n formed using lowercase English letters such that no character appears k or more times consecutively.

Return the answer modulo 10^9 + 7.

Function

stringsWithNoKConsecutiveIdenticalCharacters(n: int, k: int) → int

Examples

Example 1

n = 3k = 2return = 16250

Total strings of length 3 is 26^3 = 17576.

Invalid strings are those with at least one adjacent equal pair. For this case, the valid count is 16250.

Constraints

1 <= n <= 10^5
1 <= k < n

Problem statement

Function

Examples

Example 1

Constraints

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