Update Exercises Directory Names to Reflect Order

exercises/05_vecs/README.md

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+# Vectors
+
+Vectors are one of the most-used Rust data structures. In other programming
+languages, they'd simply be called Arrays, but since Rust operates on a
+bit of a lower level, an array in Rust is stored on the stack (meaning it
+can't grow or shrink, and the size needs to be known at compile time),
+and a Vector is stored in the heap (where these restrictions do not apply).
+
+Vectors are a bit of a later chapter in the book, but we think that they're
+useful enough to talk about them a bit earlier. We shall be talking about
+the other useful data structure, hash maps, later.
+
+## Further information
+
+- [Storing Lists of Values with Vectors](https://doc.rust-lang.org/stable/book/ch08-01-vectors.html)
+- [`iter_mut`](https://doc.rust-lang.org/std/primitive.slice.html#method.iter_mut)
+- [`map`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.map)

exercises/05_vecs/vecs1.rs

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+// vecs1.rs
+//
+// Your task is to create a `Vec` which holds the exact same elements as in the
+// array `a`.
+//
+// Make me compile and pass the test!
+//
+// Execute `rustlings hint vecs1` or use the `hint` watch subcommand for a hint.
+
+// I AM NOT DONE
+
+fn array_and_vec() -> ([i32; 4], Vec<i32>) {
+    let a = [10, 20, 30, 40]; // a plain array
+    let v = // TODO: declare your vector here with the macro for vectors
+
+    (a, v)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_array_and_vec_similarity() {
+        let (a, v) = array_and_vec();
+        assert_eq!(a, v[..]);
+    }
+}

exercises/05_vecs/vecs2.rs

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+// vecs2.rs
+//
+// A Vec of even numbers is given. Your task is to complete the loop so that
+// each number in the Vec is multiplied by 2.
+//
+// Make me pass the test!
+//
+// Execute `rustlings hint vecs2` or use the `hint` watch subcommand for a hint.
+
+// I AM NOT DONE
+
+fn vec_loop(mut v: Vec<i32>) -> Vec<i32> {
+    for element in v.iter_mut() {
+        // TODO: Fill this up so that each element in the Vec `v` is
+        // multiplied by 2.
+        ???
+    }
+
+    // At this point, `v` should be equal to [4, 8, 12, 16, 20].
+    v
+}
+
+fn vec_map(v: &Vec<i32>) -> Vec<i32> {
+    v.iter().map(|element| {
+        // TODO: Do the same thing as above - but instead of mutating the
+        // Vec, you can just return the new number!
+        ???
+    }).collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_vec_loop() {
+        let v: Vec<i32> = (1..).filter(|x| x % 2 == 0).take(5).collect();
+        let ans = vec_loop(v.clone());
+
+        assert_eq!(ans, v.iter().map(|x| x * 2).collect::<Vec<i32>>());
+    }
+
+    #[test]
+    fn test_vec_map() {
+        let v: Vec<i32> = (1..).filter(|x| x % 2 == 0).take(5).collect();
+        let ans = vec_map(&v);
+
+        assert_eq!(ans, v.iter().map(|x| x * 2).collect::<Vec<i32>>());
+    }
+}