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feat: add solutions to lc problems: No.2309~2312
* No.2309.Greatest English Letter in Upper and Lower Case * No.2310.Sum of Numbers With Units Digit K * No.2311.Longest Binary Subsequence Less Than or Equal to K * No.2312.Selling Pieces of Wood
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‎solution/2300-2399/2309.Greatest English Letter in Upper and Lower Case/README.md

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# [2309. 兼具大小写的最好英文字母](https://leetcode.cn/problems/greatest-english-letter-in-upper-and-lower-case)
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[English Version](/solution/2300-2399/2309.Greatest%20English%20Letter%20in%20Upper%20and%20Lower%20Case/README_EN.md)
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## 题目描述
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<!-- 这里写题目描述 -->
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<p>给你一个由英文字母组成的字符串 <code>s</code> ，请你找出并返回 <code>s</code> 中的 <strong>最好</strong> 英文字母。返回的字母必须为大写形式。如果不存在满足条件的字母，则返回一个空字符串。</p>
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<p><strong>最好</strong> 英文字母的大写和小写形式必须 <strong>都</strong> 在 <code>s</code> 中出现。</p>
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<p>英文字母 <code>b</code> 比另一个英文字母&nbsp;<code>a</code>&nbsp;<strong>更好</strong> 的前提是：英文字母表中，<code>b</code> 在 <code>a</code> 之 <strong>后</strong> 出现。</p>
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<p>&nbsp;</p>
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<p><strong>示例 1：</strong></p>
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<pre>
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<strong>输入：</strong>s = "l<em><strong>Ee</strong></em>TcOd<em><strong>E</strong></em>"
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<strong>输出：</strong>"E"
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<strong>解释：</strong>
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字母 'E' 是唯一一个大写和小写形式都出现的字母。</pre>
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<p><strong>示例 2：</strong></p>
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<pre>
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<strong>输入：</strong>s = "a<em><strong>rR</strong></em>AzFif"
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<strong>输出：</strong>"R"
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<strong>解释：</strong>
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字母 'R' 是大写和小写形式都出现的最好英文字母。
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注意 'A' 和 'F' 的大写和小写形式也都出现了，但是 'R' 比 'F' 和 'A' 更好。
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</pre>
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<p><strong>示例 3：</strong></p>
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<pre>
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<strong>输入：</strong>s = "AbCdEfGhIjK"
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<strong>输出：</strong>""
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<strong>解释：</strong>
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不存在大写和小写形式都出现的字母。
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</pre>
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<p>&nbsp;</p>
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<p><strong>提示：</strong></p>
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<ul>
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<li><code>1 &lt;= s.length &lt;= 1000</code></li>
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<li><code>s</code> 由小写和大写英文字母组成</li>
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</ul>
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## 解法
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<!-- 这里可写通用的实现逻辑 -->
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**方法一：哈希表 + 枚举**
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<!-- tabs:start -->
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### **Python3**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```python
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class Solution:
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def greatestLetter(self, s: str) -> str:
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ss = set(s)
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for c in ascii_uppercase[::-1]:
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if c in ss and c.lower() in ss:
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return c
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return ''
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```
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### **Java**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```java
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class Solution {
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public String greatestLetter(String s) {
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int[] cnt = new int[26];
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for (char c : s.toCharArray()) {
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if (Character.isLowerCase(c)) {
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cnt[c - 'a'] |= 1;
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} else if (Character.isUpperCase(c)) {
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cnt[c - 'A'] |= 2;
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}
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}
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for (int i = 25; i >= 0; --i) {
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if (cnt[i] == 3) {
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return String.valueOf((char) ('A' + i));
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}
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}
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return "";
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}
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}
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```
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```java
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class Solution {
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public String greatestLetter(String s) {
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Set<Character> ss = new HashSet<>();
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for (char c : s.toCharArray()) {
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ss.add(c);
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}
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for (char a = 'Z'; a >= 'A'; --a) {
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if (ss.contains(a) && ss.contains((char) (a + 32))) {
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return String.valueOf(a);
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}
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}
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return "";
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}
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}
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```
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### **C++**
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```cpp
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class Solution {
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public:
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string greatestLetter(string s) {
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unordered_set<char> ss;
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for (char& c : s) ss.insert(c);
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for (char c = 'Z'; c >= 'A'; --c)
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if (ss.count(c) && ss.count(char(c + 32)))
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return string(1, c);
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return "";
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}
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};
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```
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### **Go**
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```go
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func greatestLetter(s string) string {
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ss := map[rune]bool{}
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for _, c := range s {
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ss[c] = true
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}
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for c := 'Z'; c >= 'A'; c-- {
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if ss[c] && ss[rune(c+32)] {
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return string(c)
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}
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}
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return ""
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}
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```
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### **TypeScript**
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```ts
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```
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### **...**
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```
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```
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<!-- tabs:end -->

‎solution/2300-2399/2309.Greatest English Letter in Upper and Lower Case/README_EN.md

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# [2309. Greatest English Letter in Upper and Lower Case](https://leetcode.com/problems/greatest-english-letter-in-upper-and-lower-case)
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[中文文档](/solution/2300-2399/2309.Greatest%20English%20Letter%20in%20Upper%20and%20Lower%20Case/README.md)
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## Description
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<p>Given a string of English letters <code>s</code>, return <em>the <strong>greatest </strong>English letter which occurs as <strong>both</strong> a lowercase and uppercase letter in</em> <code>s</code>. The returned letter should be in <strong>uppercase</strong>. If no such letter exists, return <em>an empty string</em>.</p>
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<p>An English letter <code>b</code> is <strong>greater</strong> than another letter <code>a</code> if <code>b</code> appears <strong>after</strong> <code>a</code> in the English alphabet.</p>
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<p>&nbsp;</p>
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<p><strong>Example 1:</strong></p>
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<pre>
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<strong>Input:</strong> s = &quot;l<strong><u>Ee</u></strong>TcOd<u><strong>E</strong></u>&quot;
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<strong>Output:</strong> &quot;E&quot;
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<strong>Explanation:</strong>
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The letter &#39;E&#39; is the only letter to appear in both lower and upper case.
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</pre>
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<p><strong>Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> s = &quot;a<strong><u>rR</u></strong>AzFif&quot;
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<strong>Output:</strong> &quot;R&quot;
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<strong>Explanation:</strong>
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The letter &#39;R&#39; is the greatest letter to appear in both lower and upper case.
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Note that &#39;A&#39; and &#39;F&#39; also appear in both lower and upper case, but &#39;R&#39; is greater than &#39;F&#39; or &#39;A&#39;.
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</pre>
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<p><strong>Example 3:</strong></p>
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<pre>
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<strong>Input:</strong> s = &quot;AbCdEfGhIjK&quot;
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<strong>Output:</strong> &quot;&quot;
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<strong>Explanation:</strong>
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There is no letter that appears in both lower and upper case.
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</pre>
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<p>&nbsp;</p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>1 &lt;= s.length &lt;= 1000</code></li>
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<li><code>s</code> consists of lowercase and uppercase English letters.</li>
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</ul>
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## Solutions
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<!-- tabs:start -->
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### **Python3**
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```python
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class Solution:
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def greatestLetter(self, s: str) -> str:
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ss = set(s)
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for c in ascii_uppercase[::-1]:
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if c in ss and c.lower() in ss:
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return c
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return ''
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```
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### **Java**
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```java
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class Solution {
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public String greatestLetter(String s) {
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int[] cnt = new int[26];
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for (char c : s.toCharArray()) {
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if (Character.isLowerCase(c)) {
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cnt[c - 'a'] |= 1;
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} else if (Character.isUpperCase(c)) {
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cnt[c - 'A'] |= 2;
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}
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}
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for (int i = 25; i >= 0; --i) {
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if (cnt[i] == 3) {
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return String.valueOf((char) ('A' + i));
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}
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}
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return "";
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}
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}
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```
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```java
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class Solution {
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public String greatestLetter(String s) {
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Set<Character> ss = new HashSet<>();
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for (char c : s.toCharArray()) {
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ss.add(c);
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}
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for (char a = 'Z'; a >= 'A'; --a) {
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if (ss.contains(a) && ss.contains((char) (a + 32))) {
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return String.valueOf(a);
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}
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}
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return "";
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}
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}
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```
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### **C++**
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```cpp
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class Solution {
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public:
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string greatestLetter(string s) {
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unordered_set<char> ss;
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for (char& c : s) ss.insert(c);
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for (char c = 'Z'; c >= 'A'; --c)
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if (ss.count(c) && ss.count(char(c + 32)))
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return string(1, c);
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return "";
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}
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};
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```
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### **Go**
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```go
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func greatestLetter(s string) string {
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ss := map[rune]bool{}
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for _, c := range s {
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ss[c] = true
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}
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for c := 'Z'; c >= 'A'; c-- {
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if ss[c] && ss[rune(c+32)] {
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return string(c)
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}
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}
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return ""
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}
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```
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### **TypeScript**
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```ts
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```
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### **...**
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```
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```
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<!-- tabs:end -->

‎solution/2300-2399/2309.Greatest English Letter in Upper and Lower Case/Solution.cpp

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class Solution {
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public:
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string greatestLetter(string s) {
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unordered_set<char> ss;
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for (char& c : s) ss.insert(c);
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for (char c = 'Z'; c >= 'A'; --c)
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if (ss.count(c) && ss.count(char(c + 32)))
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return string(1, c);
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return "";
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}
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};

‎solution/2300-2399/2309.Greatest English Letter in Upper and Lower Case/Solution.go

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func greatestLetter(s string) string {
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ss := map[rune]bool{}
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for _, c := range s {
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ss[c] = true
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}
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for c := 'Z'; c >= 'A'; c-- {
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if ss[c] && ss[rune(c+32)] {
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return string(c)
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}
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}
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return ""
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}

‎solution/2300-2399/2309.Greatest English Letter in Upper and Lower Case/Solution.java

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class Solution {
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public String greatestLetter(String s) {
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int[] cnt = new int[26];
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for (char c : s.toCharArray()) {
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if (Character.isLowerCase(c)) {
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cnt[c - 'a'] |= 1;
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} else if (Character.isUpperCase(c)) {
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cnt[c - 'A'] |= 2;
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}
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}
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for (int i = 25; i >= 0; --i) {
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if (cnt[i] == 3) {
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return String.valueOf((char) ('A' + i));
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}
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}
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return "";
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}
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}

‎solution/2300-2399/2309.Greatest English Letter in Upper and Lower Case/Solution.py

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class Solution:
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def greatestLetter(self, s: str) -> str:
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ss = set(s)
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for c in ascii_uppercase[::-1]:
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if c in ss and c.lower() in ss:
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return c
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return ''

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