Many bug fixes and improvements (#1270)

* Add Ruby and Kotlin icons
Add the avatar of @curtishd

* Update README

* Synchronize zh-hant and zh versions.

* Translate the pythontutor blocks to traditional Chinese

* Fix en/mkdocs.yml

* Update the landing page of the en version.

* Fix the Dockerfile

* Refine the en landingpage

* Fix en landing page

* Reset the README.md

zh-hant/codes/kotlin/chapter_graph/graph_dfs.kt

@@ -15,11 +15,12 @@ fun dfs(
     res: MutableList<Vertex?>,
     vet: Vertex?
 ) {
-    res.add(vet) // 記錄訪問頂點
+    res.add(vet)     // 記錄訪問頂點
     visited.add(vet) // 標記該頂點已被訪問
     // 走訪該頂點的所有鄰接頂點
     for (adjVet in graph.adjList[vet]!!) {
-        if (visited.contains(adjVet)) continue  // 跳過已被訪問的頂點
+        if (visited.contains(adjVet))
+            continue  // 跳過已被訪問的頂點
         // 遞迴訪問鄰接頂點
         dfs(graph, visited, res, adjVet)
     }
@@ -27,14 +28,11 @@ fun dfs(
 
 /* 深度優先走訪 */
 // 使用鄰接表來表示圖，以便獲取指定頂點的所有鄰接頂點
-fun graphDFS(
-    graph: GraphAdjList,
-    startVet: Vertex?
-): List<Vertex?> {
+fun graphDFS(graph: GraphAdjList, startVet: Vertex?): MutableList<Vertex?> {
     // 頂點走訪序列
-    val res: MutableList<Vertex?> = ArrayList()
+    val res = mutableListOf<Vertex?>()
     // 雜湊表，用於記錄已被訪問過的頂點
-    val visited: MutableSet<Vertex?> = HashSet()
+    val visited = HashSet<Vertex?>()
     dfs(graph, visited, res, startVet)
     return res
 }