kth-smallest-element-in-a-bst solution

Author: sun912

kth-smallest-element-in-a-bst/sun912.py

@@ -0,0 +1,27 @@
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+
+"""
+    TC: O(n) in worst case
+    SC: O(n) in worst case
+"""
+class Solution:
+    def kthSmallest(self, root: Optional[TreeNode], k: int) -> int:
+        n = 0
+        stack = []
+        current_node = root
+
+        while current_node or stack:
+            while current_node:
+                stack.append(current_node)
+                current_node = current_node.left
+
+            current_node = stack.pop()
+            n += 1
+            if n == k:
+                return current_node.val
+            current_node = current_node.right