Add 0230-kth-smallest-element-in-a-bst.scala

Author: ChrisKheng

scala/0230-kth-smallest-element-in-a-bst.scala

@@ -0,0 +1,36 @@
+/**
+ * Definition for a binary tree node.
+ * class TreeNode(_value: Int = 0, _left: TreeNode = null, _right: TreeNode = null) {
+ *   var value: Int = _value
+ *   var left: TreeNode = _left
+ *   var right: TreeNode = _right
+ * }
+ */
+object Solution {
+    def kthSmallest(root: TreeNode, k: Int): Int = {
+        helper(root, k)._2
+    }
+
+    // Recursive in-order traversal.
+    def helper(root: TreeNode, k: Int): (Boolean, Int, Int) = {
+        if (root == null) {
+            return (false, 0, 0)
+        }
+
+        val (isInLeft, lVal, lSize) = helper(root.left, k)
+        if (isInLeft) {
+            return (true, lVal, 0)
+        } else {
+            if (k - lSize == 1) {
+                return (true, root.value, 0)
+            } else {
+                val (isInRight, rVal, rSize) = helper(root.right, k - (lSize + 1))
+                if (isInRight) {
+                    return (true, rVal, 0)
+                } else {
+                    return (false, 0, lSize + rSize + 1)
+                }
+            }
+        }
+    }
+}