[parkhojeong] WEEK 13 Solutions (#2865)

* lowest-common-ancestor-of-a-binary-search-tree solution

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

Author: parkhojeong

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

@@ -0,0 +1,21 @@
+# 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
+class Solution:
+    def kthSmallest(self, root: TreeNode | None, k: int) -> int:
+        arr = []
+
+        def inorrder(node: TreeNode):
+            if node.left:
+                inorrder(node.left)
+
+            arr.append(node.val)
+
+            if node.right:
+                inorrder(node.right)
+
+        inorrder(root)
+        return arr[k - 1]

lowest-common-ancestor-of-a-binary-search-tree/parkhojeong.py

@@ -0,0 +1,29 @@
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution:
+    def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
+
+        def search(node: TreeNode, target: int):
+            stack = [node]
+            arr = []
+            while stack:
+                node = stack.pop()
+                arr.append(node)
+                if node.val > target:
+                    stack.append(node.left)
+                elif node.val < target:
+                    stack.append(node.right)
+
+            return arr
+
+        arr1 = set(search(root, p.val))
+        arr2 = search(root, q.val)
+
+        for node in arr2[::-1]:
+            if node in arr1:
+                return node