Add solution for 230: Kth smallest element in BST

leetcode/binary_trees/230_Kth_smallest_element_in_BST/main.go

@@ -0,0 +1,22 @@
+package main
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+func traverse(root *TreeNode, res *[]int) {
+	if root == nil {
+		return
+	}
+	traverse(root.Left, res)
+	*res = append(*res, root.Val)
+	traverse(root.Right, res)
+}
+
+func kthSmallest(root *TreeNode, k int) int {
+	var result []int
+	traverse(root, &result)
+	return result[k-1]
+}