Refine kotlin code (#1241)

* style(kotlin): Improve kotlin codes readability.

* remove redundant quotes.

* style(kotlin): improve codes readability.

* style(kotlin): refine kotlin codes.

* Create kotlin.yml

* Create kotlin.yml

* Delete .github/workflows/kotlin

* Delete .github/workflows/main.yml

* Create kotlin.yml

* Update kotlin.yml

* Delete .github/workflows/kotlin.yml

* Create hello_world_workflow.main.kts

* Delete .github/workflows/hello_world_workflow.main.kts

* remove empty line

codes/kotlin/utils/PrintUtil.kt

@@ -20,7 +20,7 @@ fun <T> printMatrix(matrix: Array<Array<T>>) {
 }
 
 /* 打印矩阵（List） */
-fun <T> printMatrix(matrix: List<List<T>>) {
+fun <T> printMatrix(matrix: MutableList<MutableList<T>>) {
     println("[")
     for (row in matrix) {
         println("  $row,")
@@ -31,7 +31,7 @@ fun <T> printMatrix(matrix: List<List<T>>) {
 /* 打印链表 */
 fun printLinkedList(h: ListNode?) {
     var head = h
-    val list = ArrayList<String>()
+    val list = mutableListOf<String>()
     while (head != null) {
         list.add(head.value.toString())
         head = head.next
@@ -91,16 +91,17 @@ fun showTrunks(p: Trunk?) {
 /* 打印哈希表 */
 fun <K, V> printHashMap(map: Map<K, V>) {
     for ((key, value) in map) {
-        println(key.toString() + " -> " + value)
+        println("${key.toString()} -> $value")
     }
 }
 
 /* 打印堆 */
 fun printHeap(queue: Queue<Int>?) {
-    val list = queue?.let { ArrayList(it) }
+    val list = mutableListOf<Int?>()
+    queue?.let { list.addAll(it) }
     print("堆的数组表示：")
     println(list)
     println("堆的树状表示：")
-    val root = list?.let { TreeNode.listToTree(it) }
+    val root = TreeNode.listToTree(list)
     printTree(root)
 }

codes/kotlin/utils/TreeNode.kt

@@ -7,6 +7,7 @@
 package utils
 
 /* 二叉树节点类 */
+/* 构造方法 */
 class TreeNode(
     var value: Int // 节点值
 ) {
@@ -59,8 +60,8 @@ class TreeNode(
         }
 
         /* 将二叉树序列化为列表 */
-        fun treeToList(root: TreeNode?): List<Int?> {
-            val res = ArrayList<Int?>()
+        fun treeToList(root: TreeNode?): MutableList<Int?> {
+            val res = mutableListOf<Int?>()
             treeToListDFS(root, 0, res)
             return res
         }

codes/kotlin/utils/Vertex.kt

@@ -19,8 +19,8 @@ class Vertex(val value: Int) {
         }
 
         /* 输入顶点列表 vets ，返回值列表 vals */
-        fun vetsToVals(vets: List<Vertex?>): List<Int> {
-            val vals = ArrayList<Int>()
+        fun vetsToVals(vets: MutableList<Vertex?>): MutableList<Int> {
+            val vals = mutableListOf<Int>()
             for (vet in vets) {
                 vals.add(vet!!.value)
             }