1 files changed, 21 insertions, 0 deletions

diff --git a/nucleotide-count/src/lib.rs b/nucleotide-count/src/lib.rs
new file mode 100644
index 0000000..98b0c38
--- /dev/null
+++ b/nucleotide-count/src/lib.rs
@@ -0,0 +1,21 @@
+use maplit::hashmap;
+use std::collections::HashMap;
+
+pub fn count(nucleotide: char, dna: &str) -> Result<usize, char> {
+    nucleotide_counts(dna)?
+        .remove(&nucleotide)
+        .ok_or(nucleotide)
+}
+
+pub fn nucleotide_counts(dna: &str) -> Result<HashMap<char, usize>, char> {
+    dna.chars().fold(
+        Ok(hashmap![ 'A' => 0, 'C' => 0, 'G' => 0, 'T' => 0 ]),
+        |acc, n| match n {
+            'A' | 'C' | 'G' | 'T' => acc.map(|mut hmap| {
+                hmap.entry(n).and_modify(|e| *e += 1).or_insert(0);
+                hmap
+            }),
+            _ => Err(n),
+        },
+    )
+}