luhn

rust/luhn/src/lib.rs

@@ -0,0 +1,22 @@
+/// Check a Luhn checksum.
+pub fn is_valid(code: &str) -> bool {
+    code.chars()
+        .rev()
+        .filter(|c| !c.is_whitespace())
+        .try_fold((0, 0), |(i, sum), c| {
+            c.to_digit(10).map(|d| {
+                let added = if 1 == i % 2 {
+                    let multiplyed = d * 2;
+                    if multiplyed > 9 {
+                        multiplyed - 9
+                    } else {
+                        multiplyed
+                    }
+                } else {
+                    d
+                };
+                (i + 1, sum + added)
+            })
+        })
+        .map_or(false, |(i, sum)| i > 1 && 0 == sum % 10)
+}