3456 - Find Special Substring of Length K.

Easy

You are given a string s and an integer k.

Determine if there exists a substring of length exactly k in s that satisfies the following conditions:

• The substring consists of only one distinct character (e.g., "aaa" or "bbb").

• If there is a character immediately before the substring, it must be different from the character in the substring.

• If there is a character immediately after the substring, it must also be different from the character in the substring.

Return true if such a substring exists. Otherwise, return false.

Example 1:

Input: s = "aaabaaa", k = 3

Output: true

Explanation:

The substring s[4..6] == "aaa" satisfies the conditions.

• It has a length of 3.

• All characters are the same.

• The character before "aaa" is 'b', which is different from 'a'.

• There is no character after "aaa".

Example 2:

Input: s = "abc", k = 2

Output: false

Explanation:

There is no substring of length 2 that consists of one distinct character and satisfies the conditions.

Constraints:

• 1 <= k <= s.length <= 100

• s consists of lowercase English letters only.