feat(vec): update vec exercises

exercises/collections/vec1.rs

@@ -2,7 +2,7 @@
 // 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 the command `rustlings hint vec1` if you need hints.
+// Execute `rustlings hint vec1` or use the `hint` watch subcommand for a hint.
 
 // I AM NOT DONE
 

exercises/collections/vec2.rs

@@ -4,8 +4,7 @@
 //
 // Make me pass the test!
 //
-// Execute the command `rustlings hint vec2` if you need
-// hints.
+// Execute `rustlings hint vec2` or use the `hint` watch subcommand for a hint.
 
 // I AM NOT DONE
 
@@ -13,12 +12,21 @@ fn vec_loop(mut v: Vec<i32>) -> Vec<i32> {
     for i 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(|num| {
+        // 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::*;
@@ -30,4 +38,12 @@ mod tests {
 
         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>>());
+    }
 }