e100: Add rust impl of rearrange chars

src/od/2024e100/rearrange-chars/src/main.rs

@@ -1,3 +1,46 @@
+// Copyright (c) 2024 Xu Shaohua <shaohua@biofan.org>. All rights reserved.
+// Use of this source is governed by General Public License that can be found
+// in the LICENSE file.
+
+use std::io::{stdin, BufRead};
+
 fn main() {
-    println!("Hello, world!");
+    // 创建计数数组
+    // 读取输入, 并统计所有字母出现的次数
+    // 统计出现的最多次数
+    // 然后逆向遍历所有的次数, 并打印结果
+    let mut chars = [0_usize; 256];
+    let mut line = String::new();
+    let ret = stdin().lock().read_line(&mut line);
+    assert!(ret.is_ok());
+
+    for byte in line.trim().bytes() {
+        let index: usize = byte as usize;
+        chars[index] += 1;
+    }
+
+    let max_count: usize = chars.iter().max().copied().unwrap();
+    let mut out = Vec::new();
+
+    for count in (1..=max_count).rev() {
+        // 遍历所有的小写字母
+        for byte in b'a'..=b'z' {
+            let index = byte as usize;
+            if chars[index] == count {
+                out.push(format!("{}:{count}", char::from_u32(byte as u32).unwrap()));
+            }
+        }
+
+        // 遍历所有的大写字母
+        for byte in b'A'..=b'Z' {
+            let index = byte as usize;
+            if chars[index] == count {
+                out.push(format!("{}:{count}", char::from_u32(byte as u32).unwrap()));
+            }
+        }
+    }
+
+    // 打印结果
+    let s = out.join(";");
+    println!("{s}");
 }