feat: add the solution of Binary Tree Level Order Traversal II(107) with kotlin.

Author: relish-wang

README.md

@@ -49,8 +49,8 @@
 | [088][088-question] | [Merge Sorted Array][088-tips]                               | [✅][088-java] |              | [✅][088-kotlin] |
 | [100][100-question] | [Same Tree][100-tips]                                        | [✅][100-java] |              | [✅][100-kotlin] |
 | [101][101-question] | [Symmetric Tree][101-tips]                                   | [✅][101-java] |              | [✅][101-kotlin] |
-| [104][104-question] | [Maximum Depth of Binary Tree][104-tips]                     | [✅][104-java] |              |                  |
-| [107][107-question] | [Binary Tree Level Order Traversal II][107-tips]             | [✅][107-java] |              |                  |
+| [104][104-question] | [Maximum Depth of Binary Tree][104-tips]                     | [✅][104-java] |              | [✅][104-kotlin] |
+| [107][107-question] | [Binary Tree Level Order Traversal II][107-tips]             | [✅][107-java] |              | [✅][107-kotlin] |
 | [108][108-question] | [Convert Sorted Array to Binary Search Tree][108-tips]       | [✅][108-java] |              |                  |
 | [110][110-question] | [Balanced Binary Tree][110-tips]                             | [✅][110-java] |              |                  |
 | [111][111-question] | [Minimum Depth of Binary Tree][111-tips]                     | [✅][111-java] |              |                  |
@@ -501,4 +501,6 @@
 [088-kotlin]: ./src/_088/kotlin/Solution.kt
 [100-kotlin]: ./src/_100/kotlin/Solution.kt
 [101-kotlin]: ./src/_101/kotlin/Solution.kt
+[104-kotlin]: ./src/_104/kotlin/Solution.kt
+[107-kotlin]: ./src/_107/kotlin/Solution.kt
 [771-kotlin]: ./src/_771/kotlin/Solution.kt

src/_107/kotlin/Solution.kt

@@ -0,0 +1,37 @@
+package _107.kotlin
+
+import structure.TreeNode
+import java.util.*
+
+/**
+ * @author relish
+ * @since 2018/04/26
+ *
+ * Definition for a binary tree node.
+ * class TreeNode(var `val`: Int = 0) {
+ *     var left: TreeNode? = null
+ *     var right: TreeNode? = null
+ * }
+ */
+class Solution {
+
+    private fun turn(list: ArrayList<ArrayList<Int>>, node: TreeNode?, depth: Int) {
+        if (node == null) return
+        if (list.size <= depth) list.add(ArrayList())
+        list[depth].add(node.`val`)
+        turn(list, node.left, 1 + depth)
+        turn(list, node.right, 1 + depth)
+    }
+
+    fun levelOrderBottom(root: TreeNode?): List<List<Int>> {
+        val list = ArrayList<ArrayList<Int>>()
+        turn(list, root, 0)
+        list.reverse()
+        return list
+    }
+}
+
+fun main(args: Array<String>) {
+    val list = Solution().levelOrderBottom(TreeNode.createTestData("[3,9,20,null,null,15,7]"))
+    println(list)
+}

tips/107/README.md

@@ -98,6 +98,26 @@ class Solution {
 }
 ```
 
+kotlin(248ms/100.00%):
+```kotlin
+class Solution {
+
+    private fun turn(list: ArrayList<ArrayList<Int>>, node: TreeNode?, depth: Int) {
+        if (node == null) return
+        if (list.size <= depth) list.add(ArrayList())
+        list[depth].add(node.`val`)
+        turn(list, node.left, 1 + depth)
+        turn(list, node.right, 1 + depth)
+    }
+
+    fun levelOrderBottom(root: TreeNode?): List<List<Int>> {
+        val list = ArrayList<ArrayList<Int>>()
+        turn(list, root, 0)
+        list.reverse()
+        return list
+    }
+}
+```
 
 ## 结语