Improve readability of kotlin code (#1233)

* style(kotlin): Improve kotlin codes readability.

* remove redundant quotes.

codes/kotlin/chapter_divide_and_conquer/build_tree.kt

@@ -10,7 +10,13 @@ import utils.TreeNode
 import utils.printTree
 
 /* 构建二叉树：分治 */
-fun dfs(preorder: IntArray, inorderMap: Map<Int?, Int?>, i: Int, l: Int, r: Int): TreeNode? {
+fun dfs(
+    preorder: IntArray,
+    inorderMap: Map<Int?, Int?>,
+    i: Int,
+    l: Int,
+    r: Int
+): TreeNode? {
     // 子树区间为空时终止
     if (r - l < 0) return null
     // 初始化根节点
@@ -28,7 +34,7 @@ fun dfs(preorder: IntArray, inorderMap: Map<Int?, Int?>, i: Int, l: Int, r: Int)
 /* 构建二叉树 */
 fun buildTree(preorder: IntArray, inorder: IntArray): TreeNode? {
     // 初始化哈希表，存储 inorder 元素到索引的映射
-    val inorderMap: MutableMap<Int?, Int?> = HashMap()
+    val inorderMap = HashMap<Int?, Int?>()
     for (i in inorder.indices) {
         inorderMap[inorder[i]] = i
     }
@@ -40,8 +46,8 @@ fun buildTree(preorder: IntArray, inorder: IntArray): TreeNode? {
 fun main() {
     val preorder = intArrayOf(3, 9, 2, 1, 7)
     val inorder = intArrayOf(9, 3, 1, 2, 7)
-    println("前序遍历 = " + preorder.contentToString())
-    println("中序遍历 = " + inorder.contentToString())
+    println("前序遍历 = ${preorder.contentToString()}")
+    println("中序遍历 = ${inorder.contentToString()}")
 
     val root = buildTree(preorder, inorder)
     println("构建的二叉树为：")

codes/kotlin/chapter_divide_and_conquer/hanota.kt

@@ -9,7 +9,7 @@ package chapter_divide_and_conquer.hanota
 /* 移动一个圆盘 */
 fun move(src: MutableList<Int>, tar: MutableList<Int>) {
     // 从 src 顶部拿出一个圆盘
-    val pan: Int = src.removeAt(src.size - 1)
+    val pan = src.removeAt(src.size - 1)
     // 将圆盘放入 tar 顶部
     tar.add(pan)
 }
@@ -39,9 +39,9 @@ fun solveHanota(A: MutableList<Int>, B: MutableList<Int>, C: MutableList<Int>) {
 /* Driver Code */
 fun main() {
     // 列表尾部是柱子顶部
-    val A: MutableList<Int> = ArrayList(mutableListOf(5, 4, 3, 2, 1))
-    val B: MutableList<Int> = ArrayList()
-    val C: MutableList<Int> = ArrayList()
+    val A = mutableListOf(5, 4, 3, 2, 1)
+    val B = mutableListOf<Int>()
+    val C = mutableListOf<Int>()
     println("初始状态下：")
     println("A = $A")
     println("B = $B")
@@ -53,4 +53,4 @@ fun main() {
     println("A = $A")
     println("B = $B")
     println("C = $C")
-}
+}