Golang Leetcode 230. Kth Smallest Element in a BST.go

func kthSmallest(root *TreeNode, k int) int {
	left := countLeaf(root.Left)
	if left == k-1 {
		return root.Val
	} else if left > k-1 {
		return kthSmallest(root.Left, k)
	} else {
		return kthSmallest(root.Right, k-left-1)
	}
}

func countLeaf(root *TreeNode) int {
	if root == nil {
		return 0
	}
	return countLeaf(root.Left) + countLeaf(root.Right) + 1
}