Find whether a string contains a length-k substring that satisfies a special validity condition.
Given a string s and an integer k, determine whether there exists a substring of length k that is considered special according to the problem's validity rule.
A typical approach is to inspect all length-k substrings efficiently and check whether each one satisfies the required condition without reprocessing the entire window from scratch.
Return the required result based on whether such a substring exists.
s.k.The exact validity rule for a substring is determined by the problem statement.
k exists.1 <= k <= |s|Example 1
Input
s = "abcabc", k = 3
Output
true
Explanation
There is at least one length-3 substring that satisfies the condition.
Example 2
Input
s = "aaaa", k = 2
Output
false
Explanation
No substring of length 2 satisfies the required special condition.
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