diff --git a/sorokinfi/427.md b/sorokinfi/427.md
index 64259e8..04adbd1 100644
--- a/sorokinfi/427.md
+++ b/sorokinfi/427.md
@@ -89,4 +89,69 @@ def ht_list_all(buckets):
             all_records.append((current['name'], current['phone']))
             current = current['next']
     all_records.sort(key=lambda x: x[0])
-    return all_records
\ No newline at end of file
+    return all_records
+
+
+# 3. двоичное дерево поиска
+# узел — словарь: {'name': 'Имя', 'phone': '123', 'left': None, 'right': None}
+
+# рекурсивно или итеративно вставляет, возвращает новый корень (если корень меняется)
+def bst_insert(root, name, phone):
+    if root is None:
+        return {'name': name, 'phone': phone, 'left': None, 'right': None}
+    
+    if name < root['name']:
+        root['left'] = bst_insert(root['left'], name, phone)
+    elif name > root['name']:
+        root['right'] = bst_insert(root['right'], name, phone)
+    else:
+        root['phone'] = phone
+    return root
+
+# поиск
+def bst_find(root, name):
+    if root is None:
+        return None
+    if name == root['name']:
+        return root['phone']
+    elif name < root['name']:
+        return bst_find(root['left'], name)
+    else:
+        return bst_find(root['right'], name)
+    
+# удаление, возвращает новый корень
+def bst_delete(root, name):
+    if root is None:
+        return None
+    
+    if name < root['name']:
+        root['left'] = bst_delete(root['left'], name)
+    elif name > root['name']:
+        root['right'] = bst_delete(root['right'], name)
+    else:
+        # одна ветвь или её отсутствие
+        if root['left'] is None:
+            return root['right']
+        if root['right'] is None:
+            return root['left']
+        # две ветви
+        successor = root['right']
+        while successor['left'] is not None:
+            successor = successor['left']
+            
+        root['name'] = successor['name']
+        root['phone'] = successor['phone']
+        root['right'] = bst_delete(root['right'], successor['name'])
+        
+    return root
+
+# центрированный обход (рекурсивно собирает записи в отсортированном порядке)
+def bst_list_all(root):
+    records = []
+    def _inorder(node):
+        if node is not None:
+            _inorder(node['left'])
+            records.append((node['name'], node['phone']))
+            _inorder(node['right'])
+    _inorder(root)
+    return records
\ No newline at end of file