Create 94-Binary-Tree-Inorder-Traversal.kt

kotlin/94-binary-tree-inorder-traversal.kt

@@ -0,0 +1,37 @@
+//iterative version
+class Solution {
+    fun inorderTraversal(root: TreeNode?): List<Int> {
+        val res = ArrayList<Int>()
+        val stack = Stack<TreeNode>()
+
+        var node = root
+        while(node != null || !stack.isEmpty()){
+            while(node != null){
+                stack.push(node)
+                node = node.left
+            }
+            node = stack.pop()
+            res.add(node.`val`)
+            node = node.right
+        }
+
+        return res
+    }
+}
+
+//recursion version
+class Solution {
+    fun inorderTraversal(root: TreeNode?): List<Int> {
+        val res = ArrayList<Int>()
+
+        fun inOrder(node: TreeNode?) {
+            node?: return
+            inOrder(node.left)
+            res.add(node.`val`)
+            inOrder(node.right)
+        }
+
+        inOrder(root)
+        return res
+    }
+}