Add Python codes for the chapter

of array and linked list.

docs/chapter_array_and_linkedlist/linked_list.md

@@ -77,7 +77,18 @@ comments: true
 === "Python"
 
     ```python title=""
-    
+    """ 初始化链表 1 -> 3 -> 2 -> 5 -> 4 """
+    # 初始化各个结点 
+    n0 = ListNode(1)
+    n1 = ListNode(3)
+    n2 = ListNode(2)
+    n3 = ListNode(5)
+    n4 = ListNode(4)
+    # 构建引用指向
+    n0.next = n1
+    n1.next = n2
+    n2.next = n3
+    n3.next = n4
     ```
 
 ## 链表优点
@@ -118,7 +129,20 @@ comments: true
 === "Python"
 
     ```python title=""
-    
+    """ 在链表的结点 n0 之后插入结点 P """
+    def insert(n0, P):
+        n1 = n0.next
+        n0.next = P
+        P.next = n1
+
+    """ 删除链表的结点 n0 之后的首个结点 """
+    def remove(n0):
+        if not n0.next:
+            return
+        # n0 -> P -> n1
+        P = n0.next
+        n1 = P.next
+        n0.next = n1
     ```
 
 ## 链表缺点
@@ -148,7 +172,13 @@ comments: true
 === "Python"
 
     ```python title=""
-    
+    """ 访问链表中索引为 index 的结点 """
+    def access(head, index):
+        for _ in range(index):
+            head = head.next
+            if not head:
+                return None
+        return head
     ```
 
 **链表的内存占用多。** 链表以结点为单位，每个结点除了保存值外，还需额外保存指针（引用）。这意味着同样数据量下，链表比数组需要占用更多内存空间。
@@ -182,7 +212,15 @@ comments: true
 === "Python"
 
     ```python title=""
-    
+    """ 在链表中查找值为 target 的首个结点 """
+    def find(head, target):
+        index = 0
+        while head:
+            if head.val == target:
+                return index
+            head = head.next
+            index += 1
+        return -1
     ```
 
 ## 常见链表类型
@@ -214,7 +252,12 @@ comments: true
 === "Python"
 
     ```python title=""
-    
+    """ 双向链表结点类 """ 
+    class ListNode:
+        def __init__(self, x):
+            self.val = x      # 结点值
+            self.next = None  # 指向后继结点的指针（引用）
+            self.prev = None  # 指向前驱结点的指针（引用）
     ```
 
 ![linkedlist_common_types](linked_list.assets/linkedlist_common_types.png)