cii: Add rust implementation of word count

cii/tests/word_count.rs

@@ -0,0 +1,33 @@
+use std::collections::BTreeMap;
+use std::env;
+use std::fs::File;
+use std::io::{self, BufRead, BufReader};
+
+fn word_count(filename: &str) -> Result<(), io::Error> {
+    let fd = File::open(filename)?;
+    let reader = BufReader::new(fd);
+    let mut counts = BTreeMap::<String, usize>::new();
+
+    for line in reader.lines() {
+        let line = line?;
+        for word in line.split_ascii_whitespace() {
+            if let Some(count) = counts.get_mut(word) {
+                *count += 1;
+            } else {
+                counts.insert(word.to_owned(), 1);
+            }
+        }
+    }
+
+    for (key, value) in &counts {
+        println!("{key}: {value}");
+    }
+
+    Ok(())
+}
+
+fn main() {
+    for arg in env::args().skip(1) {
+        word_count(&arg).unwrap();
+    }
+}