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_backtracking/permutations_i.kt

@@ -11,11 +11,11 @@ fun backtrack(
     state: MutableList<Int>,
     choices: IntArray,
     selected: BooleanArray,
-    res: MutableList<List<Int>?>
+    res: MutableList<MutableList<Int>?>
 ) {
     // 當狀態長度等於元素數量時，記錄解
     if (state.size == choices.size) {
-        res.add(ArrayList(state))
+        res.add(state.toMutableList())
         return
     }
     // 走訪所有選擇
@@ -36,9 +36,9 @@ fun backtrack(
 }
 
 /* 全排列 I */
-fun permutationsI(nums: IntArray): List<List<Int>?> {
-    val res: MutableList<List<Int>?> = ArrayList()
-    backtrack(ArrayList(), nums, BooleanArray(nums.size), res)
+fun permutationsI(nums: IntArray): MutableList<MutableList<Int>?> {
+    val res = mutableListOf<MutableList<Int>?>()
+    backtrack(mutableListOf(), nums, BooleanArray(nums.size), res)
     return res
 }