LeetCode-in-Java

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:

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.

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.

Solution

@SuppressWarnings("java:S1871")
public class Solution {
    public boolean hasSpecialSubstring(String s, int k) {
        int start = 0;
        int end = k;
        while (end <= s.length()) {
            boolean flag = false;
            for (int i = start; i < end - 1; i++) {
                if (s.charAt(i) != s.charAt(i + 1)) {
                    start++;
                    end++;
                    flag = true;
                    break;
                }
            }
            if (flag) {
                continue;
            }
            if (start - 1 >= 0 && s.charAt(start) == s.charAt(start - 1)
                    || end < s.length() && s.charAt(end) == s.charAt(end - 1)) {
                start++;
                end++;
            } else {
                return true;
            }
        }
        return false;
    }
}

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