Solution 2018-14: Small improvement

Make especially part 2 better readable and
a bit more performant.

Author: rhaendel

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

@@ -7,6 +7,23 @@ import kotlin.math.abs
  */
 fun Long.digitCount(): Int {
     if (this == 0L) return 1
+    require(this >= 0)
+
+    var count = 0
+    var currentNumber = this
+    while (currentNumber > 0) {
+        currentNumber /= 10
+        count++
+    }
+    return count
+}
+
+/**
+ * Counts the number of digits of the given Int number.
+ */
+fun Int.digitCount(): Int {
+    if (this == 0) return 1
+    require(this >= 0)
 
     var count = 0
     var currentNumber = this
@@ -49,3 +66,28 @@ fun Boolean.toDigit(): String = when (this) {
     true -> "1"
     false -> "0"
 }
+
+/**
+ * @return this positive [Int]'s digits from the lowest to the highest.
+ */
+fun Int.digits(): Sequence<Int> = sequence {
+    require(this@digits >= 0)
+    var remainder = this@digits
+    if (remainder == 0) yield(0)
+    while (remainder != 0) {
+        yield(remainder % 10)
+        remainder /= 10
+    }
+}
+
+/**
+ * @return this positive [Int]'s digits from the highest to the lowest.
+ */
+fun Int.digitsReversed(): Sequence<Int> = sequence {
+    require(this@digitsReversed >= 0)
+    var factor = 10.pow(this@digitsReversed.digitCount() - 1)
+    while (factor > 0) {
+        yield((this@digitsReversed % (10 * factor) - this@digitsReversed % factor) / factor)
+        factor /= 10
+    }
+}

src/main/kotlin/de/ronny_h/aoc/year2018/day14/ChocolateCharts.kt

@@ -1,6 +1,7 @@
 package de.ronny_h.aoc.year2018.day14
 
 import de.ronny_h.aoc.AdventOfCode
+import de.ronny_h.aoc.extensions.numbers.digitsReversed
 
 fun main() = ChocolateCharts().run("5992684592", "20181148")
 
@@ -35,8 +36,8 @@ private class ScoreBoard {
         while (true) {
             val scoreOne = scores[indexOne]
             val scoreTwo = scores[indexTwo]
-            "${scoreOne + scoreTwo}".forEach {
-                scores.add(it.digitToInt())
+            (scoreOne + scoreTwo).digitsReversed().forEach {
+                scores.add(it)
                 if (stopCondition(scores)) {
                     return scores.joinToString("")
                 }

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

@@ -7,9 +7,17 @@ import io.kotest.data.row
 import io.kotest.matchers.shouldBe
 
 class DigitsTest : StringSpec({
-    "Digits are counted" {
+    "Long Digits are counted" {
         forAll(
-            row(0L, 1), row(123L, 3), row(1234567890, 10)
+            row(0L, 1), row(123L, 3), row(1234567890L, 10)
+        ) { number, digits ->
+            number.digitCount() shouldBe digits
+        }
+    }
+
+    "Int Digits are counted" {
+        forAll(
+            row(0, 1), row(123, 3), row(1234567890, 10)
         ) { number, digits ->
             number.digitCount() shouldBe digits
         }
@@ -61,4 +69,26 @@ class DigitsTest : StringSpec({
         true.toDigit() shouldBe "1"
         false.toDigit() shouldBe "0"
     }
+
+    "the digits of an Int" {
+        forAll(
+            row(0, listOf(0)),
+            row(1, listOf(1)),
+            row(123, listOf(3, 2, 1)),
+            row(1234567, listOf(7, 6, 5, 4, 3, 2, 1)),
+        ) { int, digits ->
+            int.digits().toList() shouldBe digits
+        }
+    }
+
+    "the reversed digits of an Int" {
+        forAll(
+            row(0, listOf(0)),
+            row(1, listOf(1)),
+            row(123, listOf(1, 2, 3)),
+            row(1234567, listOf(1, 2, 3, 4, 5, 6, 7)),
+        ) { int, digits ->
+            int.digitsReversed().toList() shouldBe digits
+        }
+    }
 })