From a9d70e9e4bda789377a188cf502055d2b0c4be57 Mon Sep 17 00:00:00 2001
From: malone6 <malone5@163.com>
Date: Thu, 14 Sep 2023 01:22:53 +0800
Subject: [PATCH] fix: raise error in peek() function of linkedlist_stack.py, 
 linkedlist_queue.py,  linkedlist_deque.py (#754)
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* fix: linkedlist_stack.py 中的peek方法需要判空raise Error

栈空的时候不能再 peek() 。另外由于 pop() 复用了 peek() ，栈空时返回的 None 会传递到 pop() 中的 num ，导致后续的继续执行
 self.peek.next 报错等后续问题

* Update linkedlist_stack.py

* Update linkedlist_queue.py

* Update linkedlist_deque.py

---------

Co-authored-by: Yudong Jin <krahets@163.com>
---
 codes/python/chapter_stack_and_queue/linkedlist_deque.py | 8 ++++++--
 codes/python/chapter_stack_and_queue/linkedlist_queue.py | 5 ++---
 codes/python/chapter_stack_and_queue/linkedlist_stack.py | 7 +++----
 3 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/codes/python/chapter_stack_and_queue/linkedlist_deque.py b/codes/python/chapter_stack_and_queue/linkedlist_deque.py
index aacc6928b..172034b1e 100644
--- a/codes/python/chapter_stack_and_queue/linkedlist_deque.py
+++ b/codes/python/chapter_stack_and_queue/linkedlist_deque.py
@@ -96,11 +96,15 @@ class LinkedListDeque:
 
     def peek_first(self) -> int:
         """访问队首元素"""
-        return None if self.is_empty() else self.front.val
+        if self.is_empty():
+            raise IndexError("双向队列为空")
+        return self.front.val
 
     def peek_last(self) -> int:
         """访问队尾元素"""
-        return None if self.is_empty() else self.rear.val
+        if self.is_empty():
+            raise IndexError("双向队列为空")
+        return self.rear.val
 
     def to_array(self) -> list[int]:
         """返回数组用于打印"""
diff --git a/codes/python/chapter_stack_and_queue/linkedlist_queue.py b/codes/python/chapter_stack_and_queue/linkedlist_queue.py
index 269d03c15..d08abed1b 100644
--- a/codes/python/chapter_stack_and_queue/linkedlist_queue.py
+++ b/codes/python/chapter_stack_and_queue/linkedlist_queue.py
@@ -51,9 +51,8 @@ class LinkedListQueue:
 
     def peek(self) -> int:
         """访问队首元素"""
-        if self.size() == 0:
-            print("队列为空")
-            return False
+        if self.is_empty():
+            raise IndexError("队列为空")
         return self.__front.val
 
     def to_list(self) -> list[int]:
diff --git a/codes/python/chapter_stack_and_queue/linkedlist_stack.py b/codes/python/chapter_stack_and_queue/linkedlist_stack.py
index e7f1ba46e..271770a7a 100644
--- a/codes/python/chapter_stack_and_queue/linkedlist_stack.py
+++ b/codes/python/chapter_stack_and_queue/linkedlist_stack.py
@@ -35,16 +35,15 @@ class LinkedListStack:
 
     def pop(self) -> int:
         """出栈"""
-        num: int = self.peek()
+        num = self.peek()
         self.__peek = self.__peek.next
         self.__size -= 1
         return num
 
     def peek(self) -> int:
         """访问栈顶元素"""
-        # 判空处理
-        if not self.__peek:
-            return None
+        if self.is_empty():
+            raise IndexError("栈为空")
         return self.__peek.val
 
     def to_list(self) -> list[int]: