1 files changed, 150 insertions, 0 deletions
diff --git a/solutions/18_iterators/iterators5.rs b/solutions/18_iterators/iterators5.rs
new file mode 100644
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+++ b/solutions/18_iterators/iterators5.rs
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+// Let's define a simple model to track Rustlings' exercise progress. Progress
+// will be modelled using a hash map. The name of the exercise is the key and
+// the progress is the value. Two counting functions were created to count the
+// number of exercises with a given progress. Recreate this counting
+// functionality using iterators. Try to not use imperative loops (for/while).
+
+use std::collections::HashMap;
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+enum Progress {
+    None,
+    Some,
+    Complete,
+}
+
+fn count_for(map: &HashMap<String, Progress>, value: Progress) -> usize {
+    let mut count = 0;
+    for val in map.values() {
+        if *val == value {
+            count += 1;
+        }
+    }
+    count
+}
+
+fn count_iterator(map: &HashMap<String, Progress>, value: Progress) -> usize {
+    // `map` is a hash map with `String` keys and `Progress` values.
+    // map = { "variables1": Complete, "from_str": None, … }
+    map.values().filter(|val| **val == value).count()
+}
+
+fn count_collection_for(collection: &[HashMap<String, Progress>], value: Progress) -> usize {
+    let mut count = 0;
+    for map in collection {
+        count += count_for(map, value);
+    }
+    count
+}
+
+fn count_collection_iterator(collection: &[HashMap<String, Progress>], value: Progress) -> usize {
+    // `collection` is a slice of hash maps.
+    // collection = [{ "variables1": Complete, "from_str": None, … },
+    //               { "variables2": Complete, … }, … ]
+    collection
+        .iter()
+        .map(|map| count_iterator(map, value))
+        .sum()
+}
+
+fn main() {
+    // You can optionally experiment here.
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn get_map() -> HashMap<String, Progress> {
+        use Progress::*;
+
+        let mut map = HashMap::new();
+        map.insert(String::from("variables1"), Complete);
+        map.insert(String::from("functions1"), Complete);
+        map.insert(String::from("hashmap1"), Complete);
+        map.insert(String::from("arc1"), Some);
+        map.insert(String::from("as_ref_mut"), None);
+        map.insert(String::from("from_str"), None);
+
+        map
+    }
+
+    fn get_vec_map() -> Vec<HashMap<String, Progress>> {
+        use Progress::*;
+
+        let map = get_map();
+
+        let mut other = HashMap::new();
+        other.insert(String::from("variables2"), Complete);
+        other.insert(String::from("functions2"), Complete);
+        other.insert(String::from("if1"), Complete);
+        other.insert(String::from("from_into"), None);
+        other.insert(String::from("try_from_into"), None);
+
+        vec![map, other]
+    }
+
+    #[test]
+    fn count_complete() {
+        let map = get_map();
+        assert_eq!(count_iterator(&map, Progress::Complete), 3);
+    }
+
+    #[test]
+    fn count_some() {
+        let map = get_map();
+        assert_eq!(count_iterator(&map, Progress::Some), 1);
+    }
+
+    #[test]
+    fn count_none() {
+        let map = get_map();
+        assert_eq!(count_iterator(&map, Progress::None), 2);
+    }
+
+    #[test]
+    fn count_complete_equals_for() {
+        let map = get_map();
+        let progress_states = [Progress::Complete, Progress::Some, Progress::None];
+        for progress_state in progress_states {
+            assert_eq!(
+                count_for(&map, progress_state),
+                count_iterator(&map, progress_state),
+            );
+        }
+    }
+
+    #[test]
+    fn count_collection_complete() {
+        let collection = get_vec_map();
+        assert_eq!(
+            count_collection_iterator(&collection, Progress::Complete),
+            6,
+        );
+    }
+
+    #[test]
+    fn count_collection_some() {
+        let collection = get_vec_map();
+        assert_eq!(count_collection_iterator(&collection, Progress::Some), 1);
+    }
+
+    #[test]
+    fn count_collection_none() {
+        let collection = get_vec_map();
+        assert_eq!(count_collection_iterator(&collection, Progress::None), 4);
+    }
+
+    #[test]
+    fn count_collection_equals_for() {
+        let collection = get_vec_map();
+        let progress_states = [Progress::Complete, Progress::Some, Progress::None];
+
+        for progress_state in progress_states {
+            assert_eq!(
+                count_collection_for(&collection, progress_state),
+                count_collection_iterator(&collection, progress_state),
+            );
+        }
+    }
+}