add new solutions

solutions/2/q230/solution.go

@@ -0,0 +1,35 @@
+package q230
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+func findKth(node *TreeNode, k, current int) (int, *int) {
+	if node == nil {
+		return current, nil
+	}
+
+	current, ret := findKth(node.Left, k, current)
+	if ret != nil {
+		return current, ret
+	}
+
+	current += 1
+	if current == k {
+		return current, &node.Val
+	}
+
+	return findKth(node.Right, k, current)
+}
+
+func kthSmallest(root *TreeNode, k int) int {
+	_, kth := findKth(root, k, 0)
+	if kth == nil {
+		return 0
+	}
+	return *kth
+}
+
+var _ = kthSmallest