230. Kth Smallest Element in a BST

https://leetcode.com/problems/kth-smallest-element-in-a-bst

Python

class Solution:
    def __init__(self):
        self.rank = 0
        self.result = 0

    def kthSmallest(self, root: Optional[TreeNode], k: int) -> int:
        self.rank = 0
        self.result = 0
        self._travel(root, k)
        return self.result

    def _travel(self, node, k):
        if not node:
            return self.rank

        self._travel(node.left, k)

        self.rank += 1
        if self.rank == k:
            self.result = node.val
            return

        self._travel(node.right, k)