add rust quicksort (#292)

* add rust quicksort

* remove binary search from quicksort

04_quicksort/rust/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "quicksort"
+version = "0.1.0"

04_quicksort/rust/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "quicksort"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

04_quicksort/rust/src/main.rs

@@ -0,0 +1,98 @@
+fn rec_sum(list: &[usize]) -> usize {
+    match list.get(0) {
+        Some(x) => x + rec_sum(&list[1..]),
+        None => 0,
+    }
+}
+
+fn rec_count<T>(list: &[T]) -> usize {
+    match list.get(0) {
+        Some(_) => 1 + rec_count(&list[1..]),
+        None => 0,
+    }
+}
+
+fn maximum<T: Ord>(list: &[T]) -> Option<&T> {
+    match list.get(0) {
+        Some(x) => match maximum(&list[1..]) {
+            Some(max) => {
+                if x > max {
+                    Some(x)
+                } else {
+                    Some(max)
+                }
+            }
+            None => Some(x),
+        },
+        None => None,
+    }
+}
+
+fn quicksort<T: Ord + Clone>(list: &Vec<T>) -> Vec<T> {
+    if list.len() < 2 {
+        list.to_vec()
+    } else {
+        let pivot = &list[0];
+
+        let mut less = vec![];
+        let mut greater = vec![];
+
+        for x in &list[1..] {
+            if x <= pivot {
+                less.push(x.clone());
+            } else {
+                greater.push(x.clone());
+            }
+        }
+
+        let mut new = Vec::with_capacity(list.len());
+        new.append(&mut quicksort(&less));
+        new.push(pivot.clone());
+        new.append(&mut quicksort(&greater));
+        new
+    }
+}
+
+fn main() {
+    let list = vec![10, 5, 2, 12, 3];
+
+    println!("quicksort: {:?}", quicksort(&list));
+    println!("sum: {}", rec_sum(&list));
+    println!("count: {}", rec_count(&list));
+    println!("maximum: {:?}", maximum(&list));
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn simple_rec_sum() {
+        let list = [2, 4, 6];
+        let expected = 12;
+
+        let result = rec_sum(&list);
+
+        assert_eq!(result, expected);
+    }
+
+    #[test]
+    fn simple_rec_count() {
+        let list = [2, 4, 6];
+        let expected = 3;
+
+        let result = rec_count(&list);
+
+        assert_eq!(result, expected);
+    }
+
+    #[test]
+    fn simple_maximum() {
+        let list = [2, 4, 6, 3];
+        let expected = 6;
+
+        let result = maximum(&list);
+
+        assert_eq!(result, Some(&expected));
+    }
+}