Factor out functions for converting a Digit to Boolean and vice versa

Author: rhaendel

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

@@ -21,3 +21,23 @@ fun Long.digitCount(): Int {
  * Returns the ones digit (the rightmost digit) of the given Long number.
  */
 fun Long.onesDigit(): Int = abs(this % 10).toInt()
+
+/**
+ * Converts a digit character to a boolean value.
+ * @return `true` if this is '1', `false` if this is '0'.
+ * @throws IllegalStateException if this is neither '1' nor '0'.
+ */
+fun Char.toBoolean(): Boolean = when (this) {
+    '1' -> true
+    '0' -> false
+    else -> error("must be either 0 or 1: '$this'")
+}
+
+/**
+ * Converts a boolean value to a digit character as String.
+ * @return "1" if this is `true`, "0" otherwise.
+ */
+fun Boolean.toDigit(): String = when (this) {
+    true -> "1"
+    false -> "0"
+}

src/main/kotlin/de/ronny_h/aoc/year24/day24/CrossedWires.kt

@@ -1,6 +1,7 @@
 package de.ronny_h.aoc.year24.day24
 
 import de.ronny_h.aoc.AdventOfCode
+import de.ronny_h.aoc.extensions.toDigit
 
 fun main() = CrossedWires().run(66055249060558, 0)
 
@@ -59,12 +60,7 @@ class CrossedWires: AdventOfCode<Long>(2024, 24) {
         .toLong(2)
 
     private fun Map<String, Wire>.withPrefixAsBinary(prefix: String): String = withPrefixSortedByLSBFirst(prefix)
-            .joinToString("") {
-                when (it.value) {
-                    true -> "1"
-                    false -> "0"
-                }
-            }
+        .joinToString("") { it.value.toDigit() }
 
     private fun Map<String, Wire>.withPrefixSortedByLSBFirst(prefix: String): List<Wire> = values
         .filter { it.name.startsWith(prefix) }

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

@@ -1,5 +1,6 @@
 package de.ronny_h.aoc.extensions
 
+import io.kotest.assertions.throwables.shouldThrow
 import io.kotest.core.spec.style.StringSpec
 import io.kotest.data.forAll
 import io.kotest.data.row
@@ -29,4 +30,20 @@ class DigitsTest : StringSpec({
             number.onesDigit() shouldBe ones
         }
     }
+
+    "toBoolean converts a char digit to Boolean" {
+        '0'.toBoolean() shouldBe false
+        '1'.toBoolean() shouldBe true
+    }
+
+    "toBoolean throws an Exception for illegal digits" {
+        shouldThrow<IllegalStateException> {
+            '2'.toBoolean()
+        }
+    }
+
+    "toDigit converts a Boolean to a digit String" {
+        true.toDigit() shouldBe "1"
+        false.toDigit() shouldBe "0"
+    }
 })