Improve readability of Kotlin code (#1236)

* style(kotlin): Improve kotlin codes readability.

* remove redundant quotes.

* style(kotlin): improve codes readability.

codes/kotlin/chapter_hashing/array_hash_map.kt

@@ -14,15 +14,9 @@ class Pair(
 
 /* 基于数组实现的哈希表 */
 class ArrayHashMap {
+    // 初始化数组，包含 100 个桶
     private val buckets = arrayOfNulls<Pair>(100)
 
-    init {
-        // 初始化数组，包含 100 个桶
-        for (i in 0..<100) {
-            buckets[i] = null
-        }
-    }
-
     /* 哈希函数 */
     fun hashFunc(key: Int): Int {
         val index = key % 100
@@ -52,25 +46,27 @@ class ArrayHashMap {
 
     /* 获取所有键值对 */
     fun pairSet(): MutableList<Pair> {
-        val pairSet = ArrayList<Pair>()
+        val pairSet = mutableListOf<Pair>()
         for (pair in buckets) {
-            if (pair != null) pairSet.add(pair)
+            if (pair != null)
+                pairSet.add(pair)
         }
         return pairSet
     }
 
     /* 获取所有键 */
     fun keySet(): MutableList<Int> {
-        val keySet = ArrayList<Int>()
+        val keySet = mutableListOf<Int>()
         for (pair in buckets) {
-            if (pair != null) keySet.add(pair.key)
+            if (pair != null)
+                keySet.add(pair.key)
         }
         return keySet
     }
 
     /* 获取所有值 */
     fun valueSet(): MutableList<String> {
-        val valueSet = ArrayList<String>()
+        val valueSet = mutableListOf<String>()
         for (pair in buckets) {
             pair?.let { valueSet.add(it.value) }
         }
@@ -82,7 +78,7 @@ class ArrayHashMap {
         for (kv in pairSet()) {
             val key = kv.key
             val value = kv.value
-            println("${key}->${value}")
+            println("${key} -> ${value}")
         }
     }
 }
@@ -104,7 +100,7 @@ fun main() {
 
     /* 查询操作 */
     // 向哈希表中输入键 key ，得到值 value
-    val name: String? = map.get(15937)
+    val name = map.get(15937)
     println("\n输入学号 15937 ，查询到姓名 $name")
 
     /* 删除操作 */
@@ -114,7 +110,7 @@ fun main() {
     map.print()
 
     /* 遍历哈希表 */
-    println("\n遍历键值对 Key->Value")
+    println("\n遍历键值对 Key -> Value")
     for (kv in map.pairSet()) {
         println("${kv.key} -> ${kv.value}")
     }
@@ -126,4 +122,4 @@ fun main() {
     for (value in map.valueSet()) {
         println(value)
     }
-}
+}

codes/kotlin/chapter_hashing/built_in_hash.kt

@@ -11,15 +11,15 @@ import utils.ListNode
 /* Driver Code */
 fun main() {
     val num = 3
-    val hashNum = Integer.hashCode(num)
+    val hashNum = num.hashCode()
     println("整数 $num 的哈希值为 $hashNum")
 
     val bol = true
-    val hashBol = Boolean.hashCode()
+    val hashBol = bol.hashCode()
     println("布尔量 $bol 的哈希值为 $hashBol")
 
     val dec = 3.14159
-    val hashDec = java.lang.Double.hashCode(dec)
+    val hashDec = dec.hashCode()
     println("小数 $dec 的哈希值为 $hashDec")
 
     val str = "Hello 算法"

codes/kotlin/chapter_hashing/hash_map.kt

@@ -11,7 +11,7 @@ import utils.printHashMap
 /* Driver Code */
 fun main() {
     /* 初始化哈希表 */
-    val map: MutableMap<Int, String> = HashMap()
+    val map = HashMap<Int, String>()
 
     /* 添加操作 */
     // 在哈希表中添加键值对 (key, value)

codes/kotlin/chapter_hashing/hash_map_chaining.kt

@@ -20,7 +20,7 @@ class HashMapChaining() {
         capacity = 4
         loadThres = 2.0 / 3.0
         extendRatio = 2
-        buckets = ArrayList(capacity)
+        buckets = mutableListOf()
         for (i in 0..<capacity) {
             buckets.add(mutableListOf())
         }

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 */

codes/kotlin/chapter_hashing/simple_hash.kt

@@ -6,7 +6,7 @@
 
 package chapter_hashing
 
-const val MODULUS = 10_0000_0007
+const val MODULUS = 1000000007
 
 /* 加法哈希 */
 fun addHash(key: String): Int {
@@ -48,7 +48,7 @@ fun rotHash(key: String): Int {
 fun main() {
     val key = "Hello 算法"
 
-    var hash: Int = addHash(key)
+    var hash = addHash(key)
     println("加法哈希值为 $hash")
 
     hash = mulHash(key)