leetcode: Add 2309

src/leetcode/2309.greatest-english-letter-in-upper-and-lower-case/Cargo.toml

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+[package]
+name = "lc-2309-greatest-english-letter-in-upper-and-lower-case"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[dependencies]

src/leetcode/2309.greatest-english-letter-in-upper-and-lower-case/index.md

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+
+# 
+
+[问题描述](../problems/)

src/leetcode/2309.greatest-english-letter-in-upper-and-lower-case/src/main.rs

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+// Copyright (c) 2024 Xu Shaohua <[email protected]>. All rights reserved.
+// Use of this source is governed by General Public License that can be found
+// in the LICENSE file.
+
+use std::collections::HashSet;
+
+// HashTable
+pub fn greatest_letter1(s: String) -> String {
+    debug_assert!(!s.is_empty());
+
+    // 构造字符集
+    let set: HashSet<char> = s.chars().collect();
+
+    let mut largest_letter: char = ' ';
+
+    // 遍历字符串所有的字符
+    for chr in s.chars() {
+        if (chr.is_ascii_lowercase() && set.contains(&chr.to_ascii_uppercase()))
+            || (chr.is_ascii_uppercase() && set.contains(&chr.to_ascii_lowercase()))
+        {
+            largest_letter = largest_letter.max(chr);
+        }
+    }
+    if largest_letter == ' ' {
+        String::new()
+    } else {
+        largest_letter.to_ascii_uppercase().into()
+    }
+}
+
+pub type SolutionFn = fn(String) -> String;
+
+fn check_solution(func: SolutionFn) {
+    let s = "lEeTcOdE".to_owned();
+    assert_eq!(func(s), "E".to_owned());
+
+    let s = "arRAzFif".to_owned();
+    assert_eq!(func(s), "R".to_owned());
+
+    let s = "AbCdEfGhIjK".to_owned();
+    assert_eq!(func(s), "".to_owned());
+}
+
+fn main() {
+    check_solution(greatest_letter1);
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{check_solution, greatest_letter1};
+
+    #[test]
+    fn test_greatest_letter1() {
+        check_solution(greatest_letter1);
+    }
+}