Improve readability of Kotlin code (#1236)

* style(kotlin): Improve kotlin codes readability.

* remove redundant quotes.

* style(kotlin): improve codes readability.

codes/kotlin/chapter_hashing/hash_map_open_addressing.kt

@@ -8,16 +8,21 @@ package chapter_hashing
 
 /* 开放寻址哈希表 */
 class HashMapOpenAddressing {
-    private var size: Int = 0 // 键值对数量
-    private var capacity = 4 // 哈希表容量
-    private val loadThres: Double = 2.0 / 3.0 // 触发扩容的负载因子阈值
-    private val extendRatio = 2 // 扩容倍数
-    private var buckets: Array<Pair?> // 桶数组
-    private val TOMBSTONE = Pair(-1, "-1") // 删除标记
+    private var size: Int               // 键值对数量
+    private var capacity: Int           // 哈希表容量
+    private val loadThres: Double       // 触发扩容的负载因子阈值
+    private val extendRatio: Int        // 扩容倍数
+    private var buckets: Array<Pair?>   // 桶数组
+    private val TOMBSTONE: Pair         // 删除标记
 
     /* 构造方法 */
     init {
+        size = 0
+        capacity = 4
+        loadThres = 2.0 / 3.0
+        extendRatio = 2
         buckets = arrayOfNulls(capacity)
+        TOMBSTONE = Pair(-1, "-1")
     }
 
     /* 哈希函数 */