From 0d99a3975ee0f99130e8c32059d8b6ef258d9d56 Mon Sep 17 00:00:00 2001
From: Asterisk <44215173+casnz1601@users.noreply.github.com>
Date: Sun, 10 Oct 2021 10:52:14 +0800
Subject: [PATCH] =?UTF-8?q?Update=200669.=E4=BF=AE=E5=89=AA=E4=BA=8C?=
 =?UTF-8?q?=E5=8F=89=E6=90=9C=E7=B4=A2=E6=A0=91.md?=
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补充python注释
---
 problems/0669.修剪二叉搜索树.md | 39 ++++++++++++++++++--------
 1 file changed, 28 insertions(+), 11 deletions(-)

diff --git a/problems/0669.修剪二叉搜索树.md b/problems/0669.修剪二叉搜索树.md
index 23269bb7..09a512c4 100644
--- a/problems/0669.修剪二叉搜索树.md
+++ b/problems/0669.修剪二叉搜索树.md
@@ -264,20 +264,37 @@ class Solution {
 
 ```
 
-## Python 
-
+## Python  
+**递归**
 ```python3
-
+# 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 trimBST(self, root: TreeNode, low: int, high: int) -> TreeNode:
-        if not root: return root
-        if root.val < low: 
-            return self.trimBST(root.right,low,high)  // 寻找符合区间[low, high]的节点
-        if root.val > high:
-            return self.trimBST(root.left,low,high)  // 寻找符合区间[low, high]的节点
-        root.left = self.trimBST(root.left,low,high)  // root->left接入符合条件的左孩子
-        root.right = self.trimBST(root.right,low,high)   // root->right接入符合条件的右孩子
-        return root
+        '''
+        确认递归函数参数以及返回值：返回更新后剪枝后的当前root节点
+        '''
+        # Base Case
+        if not root: return None
+
+        # 单层递归逻辑
+        if root.val < low:
+            # 若当前root节点小于左界：只考虑其右子树，用于替代更新后的其本身，抛弃其左子树整体
+            return self.trimBST(root.right, low, high)
+        
+        if high < root.val:
+            # 若当前root节点大于右界：只考虑其左子树，用于替代更新后的其本身，抛弃其右子树整体
+            return self.trimBST(root.left, low, high)
+
+        if low <= root.val <= high:
+            root.left = self.trimBST(root.left, low, high)
+            root.right = self.trimBST(root.right, low, high)
+            # 返回更新后的剪枝过的当前节点root
+            return root
 ```
 
 ## Go