3458 - Select K Disjoint Special Substrings.

Medium

Given a string s of length n and an integer k, determine whether it is possible to select k disjoint special substrings.

A special substring is a substring where:

• Any character present inside the substring should not appear outside it in the string.

• The substring is not the entire string s.

Note that all k substrings must be disjoint, meaning they cannot overlap.

Return true if it is possible to select k such disjoint special substrings; otherwise, return false.

Example 1:

Input: s = "abcdbaefab", k = 2

Output: true

Explanation:

• We can select two disjoint special substrings: "cd" and "ef".

• "cd" contains the characters 'c' and 'd', which do not appear elsewhere in s.

• "ef" contains the characters 'e' and 'f', which do not appear elsewhere in s.

Example 2:

Input: s = "cdefdc", k = 3

Output: false

Explanation:

There can be at most 2 disjoint special substrings: "e" and "f". Since k = 3, the output is false.

Example 3:

Input: s = "abeabe", k = 0

Output: true

Constraints:

• <code>2 <= n == s.length <= 5 * 10⁴</code>

• 0 <= k <= 26

• s consists only of lowercase English letters.