Add solution #230

Author: JoshCrozier

README.md

@@ -203,6 +203,7 @@
 226|[Invert Binary Tree](./0226-invert-binary-tree.js)|Easy|
 228|[Summary Ranges](./0228-summary-ranges.js)|Easy|
 229|[Majority Element II](./0229-majority-element-ii.js)|Medium|
+230|[Kth Smallest Element in a BST](./0230-kth-smallest-element-in-a-bst.js)|Medium|
 231|[Power of Two](./0231-power-of-two.js)|Easy|
 232|[Implement Queue using Stacks](./0232-implement-queue-using-stacks.js)|Easy|
 233|[Number of Digit One](./0233-number-of-digit-one.js)|Hard|

solutions/0230-kth-smallest-element-in-a-bst.js

@@ -0,0 +1,34 @@
+/**
+ * 230. Kth Smallest Element in a BST
+ * https://leetcode.com/problems/kth-smallest-element-in-a-bst/
+ * Difficulty: Medium
+ *
+ * Given the root of a binary search tree, and an integer k, return the kth smallest value
+ * (1-indexed) of all the values of the nodes in the tree.
+ */
+
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @param {number} k
+ * @return {number}
+ */
+var kthSmallest = function(root, k) {
+  const result = [];
+  dfs(root);
+  return result[k - 1];
+
+  function dfs(node) {
+    if (!node || result.length > k) return null;
+    dfs(node.left);
+    result.push(node.val);
+    dfs(node.right);
+  }
+};