finish access part

practical.yml

@@ -44,3 +44,8 @@ exercises:
     tests:
       - "add_last_two_not_enough"
       - "add_last_two_enough"
+      - "dup_top_empty"
+      - "dup_top_has_value"
+      - "median_already_sorted"
+      - "median_shuffled"
+      - "median_empty"

subject_source/src/vec/access.rs

@@ -1,10 +1,37 @@
 /// Add the last two numbers of the input slice.
 ///
-/// If the slice is not large enough, return `None`
-/// If it is, return the computed value in a `Some`
+/// # Return value
+/// `None` if the slice is not large enough
+/// `Some(result)` if the slice has at least 2 elements
 pub fn add_last_two(v: &[f32]) -> Option<f32> {
     match v.last_chunk() {
         Some([a, b]) => Some(a + b),
         None => None,
     }
 }
+
+/// Duplicate the top element from the stack if it exist
+/// (the stack is represented as a Vec with top == last)
+///
+/// # Return value
+/// `Some(())` if the operation succeeded
+/// `None` if not
+pub fn dup_top(v: &mut Vec<f32>) -> Option<()> {
+    match v.last() {
+        Some(last) => {
+            v.push(*last);
+            return Some(());
+        }
+        _ => return None,
+    }
+}
+
+/// Compute the median of a slice in place (if the slice was sorted, it would be the middle element)
+pub fn median(v: &[i32]) -> Option<i32> {
+    let mut tmp = v.to_vec();
+    tmp.sort();
+    match tmp.get(tmp.len() / 2) {
+        Some(&r) => Some(r),
+        None => None,
+    }
+}

subject_source/tests/vec_access.rs

@@ -9,3 +9,31 @@ pub fn add_last_two_not_enough() {
 pub fn add_last_two_enough() {
     assert_eq!(access::add_last_two(&[1.0, 2.0, 3.0]), Some(5.0));
 }
+
+#[test]
+pub fn dup_top_empty() {
+    let mut empty = vec![];
+    assert!(access::dup_top(&mut empty).is_none());
+}
+
+#[test]
+pub fn dup_top_has_values() {
+    let mut empty = vec![1.0, 2.0];
+    assert!(access::dup_top(&mut empty).is_some());
+    assert_eq!(empty, &[1.0, 2.0, 2.0]);
+}
+
+#[test]
+pub fn median_already_sorted() {
+    assert_eq!(access::median(&[1, 2, 3]), Some(2));
+}
+
+#[test]
+pub fn median_shuffled() {
+    assert_eq!(access::median(&[420, 69, 128]), Some(128));
+}
+
+#[test]
+pub fn median_empty() {
+    assert_eq!(access::median(&[]), None);
+}

subject_text/vec/access.md

@@ -0,0 +1,60 @@
+---
+name = "Accessing values"
+file = "src/vec/access.rs"
+---
+
+Instead of using the good old C-style bound checking:
+
+```rust
+if vec.len() < 1 {
+    return None;
+} else {
+    // compiler still thinks this line can panic
+    return vec[0];
+}
+```
+
+Try to implement these functions using non-panicking methods like [`last`](https://doc.rust-lang.org/std/primitive.slice.html#method.last), [`last_chunk`](https://doc.rust-lang.org/std/primitive.slice.html#method.last_chunk), or [`get`](https://doc.rust-lang.org/std/primitive.slice.html#method.get).
+
+```prototype
+/// Add the last two numbers of the input slice.
+///
+/// # Return value
+/// `None` if the slice is not large enough
+/// `Some(result)` if the slice has at least 2 elements
+pub fn add_last_two(v: &[f32]) -> Option<f32> {
+    unimplemented!()
+}
+
+/// Duplicate the top element from the stack if it exist
+/// (the stack is represented as a Vec with top == last)
+///
+/// # Return value
+/// `Some(())` if the operation succeeded
+/// `None` if not
+pub fn dup_top(v: &mut Vec<f32>) -> Option<()> {
+    unimplemented!()
+}
+
+/// Compute the median of a slice in place (if the slice was sorted, it would be the middle element)
+pub fn median(v: &[i32]) -> Option<i32> {
+    unimplemented!()
+}
+```
+
+```example
+fn main() {
+    assert_eq!(add_last_two(&[]), None);
+    assert_eq!(add_last_two(&[10.0]), None);
+    assert_eq!(add_last_two(&[1.0, 2.0, 3.0]), Some(5.0));
+
+    let mut stack = vec![1.0];
+    assert!(dup_top(&mut stack).is_some());
+    assert_eq!(&stack, &[1.0, 1.0]);
+
+    stack.clear();
+    assert!(dup_top(&mut stack).is_none());
+
+    assert_eq!(median(&[2, 1, 3]), Some(2));
+}
+```

subject_text/vec/index.md

@@ -14,21 +14,3 @@ Slices (`[T]`) represent some memory space containing an arbitrary number of ele
 `Vec<T>` can be seen as [owned](https://doc.rust-lang.org/book/ch04-00-understanding-ownership.html) `[T]`, it means that every function working on a `&[T]` can work on a `&Vec<T>`.
 ```
 
-```prototype
-/// Add the last two numbers of the input slice.
-///
-/// If the slice is not large enough, return `None`
-/// If it is, return the computed value in a `Some`
-pub fn add_last_two(v: &[f32]) -> Option<f32> {
-    unimplemented!()
-}
-```
-
-```example
-fn main() {
-    assert_eq!(add_last_two(&[]), None);
-    assert_eq!(add_last_two(&[10.0]), None);
-    assert_eq!(add_last_two(&[1.0, 2.0, 3.0]), Some(5.0));
-}
-```
-