find-longest-special-substring-that-occurs-thrice-i

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Algorithms

You are given a string <code>s</code> that consists of lowercase English letters.

A string is called special if it is made up of only a single character. For example, the string <code>&quot;abc&quot;</code> is not special, whereas the strings <code>&quot;ddd&quot;</code>, <code>&quot;zz&quot;</code>, and <code>&quot;f&quot;</code> are special.

Return the length of the longest special substring of <code>s</code> which occurs at least thrice, or <code>-1</code> if no special substring occurs at least thrice.

A substring is a contiguous non-empty sequence of characters within a string.

&nbsp;
Example 1:

<pre>
Input: s = &quot;aaaa&quot;
Output: 2
Explanation: The longest special substring which occurs thrice is &quot;aa&quot;: substrings &quot;aaaa&quot;, &quot;aaaa&quot;, and &quot;aaaa&quot;.
It can be shown that the maximum length achievable is 2.
</pre>

Example 2:

<pre>
Input: s = &quot;abcdef&quot;
Output: -1
Explanation: There exists no special substring which occurs at least thrice. Hence return -1.
</pre>

Example 3:

<pre>
Input: s = &quot;abcaba&quot;
Output: 1
Explanation: The longest special substring which occurs thrice is &quot;a&quot;: substrings &quot;abcaba&quot;, &quot;abcaba&quot;, and &quot;abcaba&quot;.
It can be shown that the maximum length achievable is 1.
</pre>

&nbsp;
Constraints:

<ul>
	<li><code>3 &lt;= s.length &lt;= 50</code></li>
	<li><code>s</code> consists of only lowercase English letters.</li>
</ul>

maximumLength

Find Longest Special Substring That Occurs Thrice I

Longest Substring Without Repeating Characters

longest-substring-without-repeating-characters

无重复字符的最长子串

Longest Substring with At Least K Repeating Characters

longest-substring-with-at-least-k-repeating-characters

至少有 K 个重复字符的最长子串

Hash Table

String

Binary Search

Counting

Sliding Window

给你一个仅由小写英文字母组成的字符串 <code>s</code> 。

如果一个字符串仅由单一字符组成，那么它被称为 特殊 字符串。例如，字符串 <code>"abc"</code> 不是特殊字符串，而字符串 <code>"ddd"</code>、<code>"zz"</code> 和 <code>"f"</code> 是特殊字符串。

返回在 <code>s</code> 中出现 至少三次 的 最长特殊子字符串 的长度，如果不存在出现至少三次的特殊子字符串，则返回 <code>-1</code> 。

子字符串 是字符串中的一个连续 非空 字符序列。

&nbsp;

示例 1：

<pre>
输入：s = "aaaa"
输出：2
解释：出现三次的最长特殊子字符串是 "aa" ：子字符串 "aaaa"、"aaaa" 和 "aaaa"。
可以证明最大长度是 2 。
</pre>

示例 2：

<pre>
输入：s = "abcdef"
输出：-1
解释：不存在出现至少三次的特殊子字符串。因此返回 -1 。
</pre>

示例 3：

<pre>
输入：s = "abcaba"
输出：1
解释：出现三次的最长特殊子字符串是 "a" ：子字符串 "abcaba"、"abcaba" 和 "abcaba"。
可以证明最大长度是 1 。
</pre>

&nbsp;

提示：

<ul>
	<li><code>3 &lt;= s.length &lt;= 50</code></li>
	<li><code>s</code> 仅由小写英文字母组成。</li>
</ul>