applied code review suggestions

exercises/practice/nucleotide-count/.approaches/groupby-plus/content.md

@@ -11,23 +11,35 @@ class Dna(val sequence: String) {
 ```
 
 ## Verification
-We receive a sequence as input, which we have to verificate.
+We receive a sequence as input, which we have to verify.
 Because the sequence is part of the primary constructor, which can't contain runnable code, we have to place the check in an [_initializer block_][stdlib-constructors].
 In Kotlin it's idiomatic to use the [`require`][stdlib-require] keyword for verification.
 `require` will throw an `IllegalArgumentException` if the given value is `false`.
+```kotlin
+init {
+    require(sequence.all { it in "ACGT" })
+}
+```
 
 ## Base Map
 We define a base map with a zero value for every nucleotide.
 We do this to ensure that every nucleotide will be present in the output, even if there is no count.
 Afterward we can overwrite some of the values by using the `+` operator.
 Note that the [`+` operator on maps][map-plus] does not add the values but overwrites them.
+```kotlin
+val nucleotideCounts
+    get() = mapOf('A' to 0, 'C' to 0, 'G' to 0, 'T' to 0)
+```
 
 ## Counting Nucleotides
 We use the `.groupingBy` function to create a [`Grouping`][stdlib-grouping] of the nucleotides.
 By using the `.eachCount()` function we turn the [`Grouping`][stdlib-grouping] in a Map.
 For example: `"ACA".groupingBy { it }.eachCount()` results in `{A=2, C=1}`.
 After [adding][map-plus] the maps together we receive our final answer.
-
+```kotlin
+val nucleotideCounts
+    get() = mapOf('A' to 0, 'C' to 0, 'G' to 0, 'T' to 0) + sequence.groupingBy { it }.eachCount()
+```
 
 [stdlib-require]: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/require.html
 [stdlib-constructors]: https://kotlinlang.org/docs/classes.html#constructors

exercises/practice/nucleotide-count/.approaches/introduction.md

@@ -9,7 +9,6 @@ Each solution has to contain the following three elements:
 One approach is to use `groupBy` and the `+` operator:
 ```kotlin
 class Dna(val sequence: String) {
-
     init {
         require(sequence.all { it in "ACGT" })
     }