Improve the consistency between code and comments in Kotlin (#1268)

* style(kotlin): Make code and comments consistent.

* style(kotlin): convert comment location.

* style(c): Add missing comment.

* style(kotlin): Remove redundant semicolon, parenthesis and brace

* style(kotlin): Put constants inside the function.

* style(kotlin): fix unnecessary indentation.

* style(swift): Add missing comment.

* style(kotlin): Add missing comment.

* style(kotlin): Remove redundant comment.

* style(kotlin): Add missing comment.

* Update linked_list.kt

* style(csharp,js,ts): Add missing comment.

* style(kotlin): Remove empty lines.

* Update list.cs

* Update list.js

* Update list.ts

* roll back to commit 1

* style(cs,js,ts): Add missing comment in docfile.

* style(kotlin): Use normal element swapping instead of scope functions.

codes/kotlin/chapter_hashing/array_hash_map.kt

@@ -68,7 +68,8 @@ class ArrayHashMap {
     fun valueSet(): MutableList<String> {
         val valueSet = mutableListOf<String>()
         for (pair in buckets) {
-            pair?.let { valueSet.add(it._val) }
+            if (pair != null)
+                valueSet.add(pair._val)
         }
         return valueSet
     }
@@ -78,7 +79,7 @@ class ArrayHashMap {
         for (kv in pairSet()) {
             val key = kv.key
             val _val = kv._val
-            println("${key} -> ${_val}")
+            println("$key -> $_val")
         }
     }
 }