From 388eeb5c4aef5497d5f55efdb4a702c38f4b5d40 Mon Sep 17 00:00:00 2001
From: kitaken <83747835+Kitaken0107@users.noreply.github.com>
Date: Sat, 23 Mar 2024 16:22:21 +0900
Subject: [PATCH] Create 10_Lowest Common Ancestor of a Binary Search Tree.md

---
 ...Common Ancestor of a Binary Search Tree.md | 41 +++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 10_Lowest Common Ancestor of a Binary Search Tree.md

diff --git a/10_Lowest Common Ancestor of a Binary Search Tree.md b/10_Lowest Common Ancestor of a Binary Search Tree.md
new file mode 100644
index 0000000..48c655f
--- /dev/null
+++ b/10_Lowest Common Ancestor of a Binary Search Tree.md	
@@ -0,0 +1,41 @@
+235. Lowest Common Ancestor of a Binary Search Tree   
+https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/
+
+0:BSTの知識不足と問題の論理が難しかった   
+方針:   
+操作としては、p・qのノードから上のノードにたどって、   
+初めて合流したときのノードがアウトプット   
+ただ上のノードをどのようにたどるかがわからない      
+
+1st   
+以下の解答を参考にしました   
+方針：rootから初めて、LCAでなければ進めて、止まったらLCAを返す(値の条件をうまく使う)
+・LCAの条件は2パターン
+　・LCAがp・qどちらかのパターン
+　・LCAがp・qの共通の親
+・なので、LCAではない条件は以下となる
+　・LCA候補が<p,q or >p,q
+
+https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/discuss/4276179/Beats-99-or-O(-log(n))-or-(Step-by-step-explanation)   
+
+```python
+# 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':
+        
+        while root:
+            if root.val > p.val and root.val > q.val:
+                root = root.left
+            elif root.val < p.val and root.val < q.val:
+                root = root.right
+            else:
+                return root
+```
+
+