{ "data": { "question": { "questionId": "1873", "questionFrontendId": "1763", "categoryTitle": "Algorithms", "boundTopicId": 607400, "title": "Longest Nice Substring", "titleSlug": "longest-nice-substring", "content": "

A string s is nice if, for every letter of the alphabet that s contains, it appears both in uppercase and lowercase. For example, "abABB" is nice because 'A' and 'a' appear, and 'B' and 'b' appear. However, "abA" is not because 'b' appears, but 'B' does not.

\n\n

Given a string s, return the longest substring of s that is nice. If there are multiple, return the substring of the earliest occurrence. If there are none, return an empty string.

\n\n

 

\n

Example 1:

\n\n
\nInput: s = "YazaAay"\nOutput: "aAa"\nExplanation: "aAa" is a nice string because 'A/a' is the only letter of the alphabet in s, and both 'A' and 'a' appear.\n"aAa" is the longest nice substring.\n
\n\n

Example 2:

\n\n
\nInput: s = "Bb"\nOutput: "Bb"\nExplanation: "Bb" is a nice string because both 'B' and 'b' appear. The whole string is a substring.\n
\n\n

Example 3:

\n\n
\nInput: s = "c"\nOutput: ""\nExplanation: There are no nice substrings.\n
\n\n

 

\n

Constraints:

\n\n\n", "translatedTitle": "最长的美好子字符串", "translatedContent": "

当一个字符串 s 包含的每一种字母的大写和小写形式 同时 出现在 s 中，就称这个字符串 s 是 美好 字符串。比方说，\"abABB\" 是美好字符串，因为 'A' 和 'a' 同时出现了，且 'B' 和 'b' 也同时出现了。然而，\"abA\" 不是美好字符串因为 'b' 出现了，而 'B' 没有出现。

\n\n

给你一个字符串 s ，请你返回 s 最长的 美好子字符串 。如果有多个答案，请你返回 最早 出现的一个。如果不存在美好子字符串，请你返回一个空字符串。

\n\n

 

\n\n

示例 1：

\n\n
\n输入：s = \"YazaAay\"\n输出：\"aAa\"\n解释：\"aAa\" 是一个美好字符串，因为这个子串中仅含一种字母，其小写形式 'a' 和大写形式 'A' 也同时出现了。\n\"aAa\" 是最长的美好子字符串。\n
\n\n

示例 2：

\n\n
\n输入：s = \"Bb\"\n输出：\"Bb\"\n解释：\"Bb\" 是美好字符串，因为 'B' 和 'b' 都出现了。整个字符串也是原字符串的子字符串。
\n\n

示例 3：

\n\n
\n输入：s = \"c\"\n输出：\"\"\n解释：没有美好子字符串。
\n\n

示例 4：

\n\n
\n输入：s = \"dDzeE\"\n输出：\"dD\"\n解释：\"dD\" 和 \"eE\" 都是最长美好子字符串。\n由于有多个美好子字符串，返回 \"dD\" ，因为它出现得最早。
\n\n

 

\n\n

提示：

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