Parallel Letter Frequency

rust/parallel-letter-frequency/src/lib.rs

@@ -0,0 +1,41 @@
+use std::any::Any;
+use std::collections::HashMap;
+use std::thread;
+
+pub fn frequency(input: &[&str], worker_count: usize) -> HashMap<char, usize> {
+    if input.is_empty() {
+        return HashMap::<char, usize>::new();
+    }
+
+    let worker_count = worker_count.max(1);
+
+    thread::scope(|s| {
+        let chunk_size = input.len().div_ceil(worker_count);
+        let mut handles: Vec<_> = input
+            .chunks(chunk_size)
+            .map(|chunk| {
+                s.spawn(move || {
+                    let mut proxy_map = HashMap::new();
+                    chunk
+                        .iter()
+                        .flat_map(|line| line.chars())
+                        .filter(|char| char.is_alphabetic())
+                        .flat_map(|char_slice| char_slice.to_lowercase())
+                        .for_each(|char| {
+                            *proxy_map.entry(char).or_insert(0) += 1;
+                        });
+                    proxy_map
+                })
+            })
+            .collect();
+        handles
+            .into_iter()
+            .map(|x| x.join().unwrap())
+            .fold(HashMap::new(), |mut acc, map| {
+                for (char, count) in map {
+                    *acc.entry(char).or_insert(0) += count;
+                }
+                acc
+            })
+    })
+}