tracks/rust/exercises/nucleotide-count/example.rs in trackler-2.0.6.3 vs tracks/rust/exercises/nucleotide-count/example.rs in trackler-2.0.6.4

@@ -1,13 +1,24 @@
 use std::collections::HashMap;
 
-pub fn count(nucleotide: char, input: &str) -> usize {
-    input.chars().filter(|&c| c == nucleotide).count()
+static VALID_NUCLEOTIDES: &'static str = "ACGT";
+
+pub fn count(nucleotide: char, input: &str) -> Result<usize, char> {
+    let valid = |x: char| { VALID_NUCLEOTIDES.contains(x) };
+    if valid(nucleotide) && input.chars().all(valid) {
+        Ok(input.chars().filter(|&c| c == nucleotide).count())
+    } else {
+        Err(nucleotide)
+    }
 }
 
-pub fn nucleotide_counts(input: &str) -> HashMap<char, usize> {
-    let mut map: HashMap<char, usize> = "ACGT".chars().map(|c| (c, 0)).collect();
+pub fn nucleotide_counts(input: &str) -> Result<HashMap<char, usize>, char> {
+    let mut map: HashMap<char, usize> = VALID_NUCLEOTIDES.chars().map(|c| (c, 0)).collect();
     for nucleotide in input.chars() {
-        *map.entry(nucleotide).or_insert(0) += 1;
+        if let Some(n) = map.get_mut(&nucleotide) {
+            *n += 1;
+        } else {
+            return Err(nucleotide);
+        }
     }
-    map
+    Ok(map)
 }