update: 230

Author: hijiangtao

README.md

@@ -131,6 +131,7 @@ This is the solutions collection of my LeetCode submissions, most of them are pr
 | 219 | [Contains Duplicate II](https://leetcode.com/problems/contains-duplicate-ii/) | [JavaScript](./src/contains-duplicate-ii/res.js) | Easy |
 | 220 | [Contains Duplicate III](https://leetcode.com/problems/contains-duplicate-iii/) | [JavaScript](./src/contains-duplicate-iii/res.js) | Medium |
 | 228 | [Summary Ranges](https://leetcode.com/problems/summary-ranges/solution/) | [JavaScript](./src/summary-ranges/res.js) | Medium |
+| 230 | [kth-smallest-element-in-a-bst](https://leetcode.com/problems/kth-smallest-element-in-a-bst/solution/) | [TypeScript](./src/kth-smallest-element-in-a-bst/res.ts) | Medium |
 | 238 | [Product of Array Except Self](https://leetcode.com/problems/product-of-array-except-self/solution/) | [JavaScript](./src/product-of-array-except-self/res.js) | Medium |
 | 239 | [Sliding Window Maximum](https://leetcode.com/problems/sliding-window-maximum/description/) | [JavaScript](./src/sliding-window-maximum/description/res.js) | Hard |
 | 240 | [Search a 2D Matrix II](https://leetcode.com/problems/search-a-2d-matrix-ii/) | [JavaScript](./src/search-a-2d-matrix-ii/res.js) · [TypeScript](./src/search-a-2d-matrix-ii/res.ts) | Medium |

src/kth-smallest-element-in-a-bst/res.ts

@@ -0,0 +1,33 @@
+/**
+* Definition for a binary tree node.
+* class TreeNode {
+* val: number
+* left: TreeNode | null
+* right: TreeNode | null
+* constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+* this.val = (val===undefined ? 0 : val)
+* this.left = (left===undefined ? null : left)
+* this.right = (right===undefined ? null : right)
+* }
+* }
+*/
+
+const getTreeList = (root: TreeNode | null): number[] => {
+if (!root) {
+return [];
+}
+
+const result = [];
+
+result.push(...getTreeList(root.left));
+result.push(root.val);
+result.push(...getTreeList(root.right));
+
+return result;
+}
+
+function kthSmallest(root: TreeNode | null, k: number): number {
+const result = getTreeList(root);
+
+return result[k-1];
+};