3456. Find Special Substring of Length K

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:

1. The substring consists of only one distinct character (e.g., "aaa" or "bbb").
2. If there is a character immediately before the substring, it must be different from the character in the substring.
3. 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.

class Solution {
public:
    bool hasSpecialSubstring(string s, int k) {
        int n = s.length();
        for(int i = 1, cnt = 1; i < n; i++) {
            if(s[i] == s[i-1]) ++cnt;
            else {
                if(cnt == k) return true;
                cnt = 1;
            }
            if(i + 1 == n and cnt == k) return true;
        }
        return n == 1;
    }
};