Python函数-在链表的开头和结尾处插入一个值-不修改链表

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

def insertAtBeginning(head, value):
    new_node = ListNode(value)
    new_node.next = head
    return new_node

def insertAtEnd(head, value):
    new_node = ListNode(value)
    if head is None:
        return new_node
    current = head
    while current.next:
        current = current.next
    current.next = new_node
    return head

# 创建链表：1 -> 2 -> 3 -> None
head = ListNode(1)
node2 = ListNode(2)
node3 = ListNode(3)
head.next = node2
node2.next = node3

# 在链表开头插入值 0
head = insertAtBeginning(head, 0)

# 在链表结尾插入值 4
head = insertAtEnd(head, 4)

# 打印链表：0 -> 1 -> 2 -> 3 -> 4 -> None
current = head
while current:
    print(current.val, end=" -> ")
    current = current.next
print("None")