3 files changed, 72 insertions, 17 deletions

diff --git a/exercises/18_iterators/iterators2.rs b/exercises/18_iterators/iterators2.rs
index 8d8909b..5903e65 100644
--- a/exercises/18_iterators/iterators2.rs
+++ b/exercises/18_iterators/iterators2.rs
@@ -1,31 +1,28 @@
 // In this exercise, you'll learn some of the unique advantages that iterators
-// can offer. Follow the steps to complete the exercise.
+// can offer.
 
-// Step 1.
-// Complete the `capitalize_first` function.
+// TODO: Complete the `capitalize_first` function.
 // "hello" -> "Hello"
 fn capitalize_first(input: &str) -> String {
-    let mut c = input.chars();
-    match c.next() {
+    let mut chars = input.chars();
+    match chars.next() {
         None => String::new(),
-        Some(first) => ???,
+        Some(first) => todo!(),
     }
 }
 
-// Step 2.
-// Apply the `capitalize_first` function to a slice of string slices.
+// TODO: Apply the `capitalize_first` function to a slice of string slices.
 // Return a vector of strings.
 // ["hello", "world"] -> ["Hello", "World"]
 fn capitalize_words_vector(words: &[&str]) -> Vec<String> {
-    vec![]
+    // ???
 }
 
-// Step 3.
-// Apply the `capitalize_first` function again to a slice of string slices.
-// Return a single string.
+// TODO: Apply the `capitalize_first` function again to a slice of string
+// slices. Return a single string.
 // ["hello", " ", "world"] -> "Hello World"
 fn capitalize_words_string(words: &[&str]) -> String {
-    String::new()
+    // ???
 }
 
 fn main() {
diff --git a/rustlings-macros/info.toml b/rustlings-macros/info.toml
index 5e93986..5a33788 100644
--- a/rustlings-macros/info.toml
+++ b/rustlings-macros/info.toml
@@ -894,7 +894,7 @@ https://doc.rust-lang.org/std/iter/trait.Iterator.html"""
 name = "iterators2"
 dir = "18_iterators"
 hint = """
-Step 1:
+`capitalize_first`:
 
 The variable `first` is a `char`. It needs to be capitalized and added to the
 remaining characters in `c` in order to return the correct `String`.
@@ -905,12 +905,15 @@ The remaining characters in `c` can be viewed as a string slice using the
 The documentation for `char` contains many useful methods.
 https://doc.rust-lang.org/std/primitive.char.html
 
-Step 2:
+Use `char::to_uppercase`. It returns an iterator that can be converted to a
+`String`.
+
+`capitalize_words_vector`:
 
 Create an iterator from the slice. Transform the iterated values by applying
 the `capitalize_first` function. Remember to `collect` the iterator.
 
-Step 3:
+`capitalize_words_string`:
 
 This is surprisingly similar to the previous solution. `collect` is very
 powerful and very general. Rust just needs to know the desired type."""
diff --git a/solutions/18_iterators/iterators2.rs b/solutions/18_iterators/iterators2.rs
index 4e18198..db05f29 100644
--- a/solutions/18_iterators/iterators2.rs
+++ b/solutions/18_iterators/iterators2.rs
@@ -1 +1,56 @@
-// Solutions will be available before the stable release. Thank you for testing the beta version 🥰
+// In this exercise, you'll learn some of the unique advantages that iterators
+// can offer.
+
+// "hello" -> "Hello"
+fn capitalize_first(input: &str) -> String {
+    let mut chars = input.chars();
+    match chars.next() {
+        None => String::new(),
+        Some(first) => first.to_uppercase().to_string() + chars.as_str(),
+    }
+}
+
+// Apply the `capitalize_first` function to a slice of string slices.
+// Return a vector of strings.
+// ["hello", "world"] -> ["Hello", "World"]
+fn capitalize_words_vector(words: &[&str]) -> Vec<String> {
+    words.iter().map(|word| capitalize_first(word)).collect()
+}
+
+// Apply the `capitalize_first` function again to a slice of string
+// slices. Return a single string.
+// ["hello", " ", "world"] -> "Hello World"
+fn capitalize_words_string(words: &[&str]) -> String {
+    words.iter().map(|word| capitalize_first(word)).collect()
+}
+
+fn main() {
+    // You can optionally experiment here.
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_success() {
+        assert_eq!(capitalize_first("hello"), "Hello");
+    }
+
+    #[test]
+    fn test_empty() {
+        assert_eq!(capitalize_first(""), "");
+    }
+
+    #[test]
+    fn test_iterate_string_vec() {
+        let words = vec!["hello", "world"];
+        assert_eq!(capitalize_words_vector(&words), ["Hello", "World"]);
+    }
+
+    #[test]
+    fn test_iterate_into_string() {
+        let words = vec!["hello", " ", "world"];
+        assert_eq!(capitalize_words_string(&words), "Hello World");
+    }
+}