An extension function to get the ones digit of a Long value

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/extensions/Digits.kt

@@ -1,5 +1,7 @@
 package de.ronny_h.aoc.extensions
 
+import kotlin.math.abs
+
 /**
  * Counts the number of digits of the given Long number.
  */
@@ -14,3 +16,8 @@ fun Long.digitCount(): Int {
     }
     return count
 }
+
+/**
+ * Returns the ones digit (the rightmost digit) of the given Long number.
+ */
+fun Long.onesDigit(): Int = abs(this % 10).toInt()

src/test/kotlin/de/ronny_h/aoc/extensions/DigitsTest.kt

@@ -13,4 +13,20 @@ class DigitsTest : StringSpec({
             number.digitCount() shouldBe digits
         }
     }
+
+    "The ones digit is returned" {
+        forAll(
+            row(0, 0),
+            row(123L, 3),
+            row(15887950, 0),
+            row(16495136, 6),
+            row(527345, 5),
+            row(-123L, 3),
+            row(-15887950, 0),
+            row(-16495136, 6),
+            row(-527345, 5),
+        ) { number, ones ->
+            number.onesDigit() shouldBe ones
+        }
+    }
 })