【数据结构专项】链表(6) —— 管理单向链表的基本类(包含头结点)

class SinglyLinkedList:
    """管理单向链表的基本类(使用头结点)"""

    class _Node:
        __slots__ = "value", "next"  # 因为会创建很多个结点对象，因此使用__slots__来减少内存占用

        def __init__(self, value, next=None):
            self.value = value
            self.next = next

        def __str__(self):
            return str(self.value) + "->" + str(self.next)

    def __init__(self):
        self._head = self._Node(None)
        self._size = 0

    def __len__(self):
        """返回链表中元素的数量"""
        return self._size

    def is_empty(self):
        """返回链表是否为空"""
        return self._size == 0

    def get(self, index: int):
        """依据座标读取变量"""
        if index < 0 or index >= self._size:
            return -1
        curr = self._head
        for _ in range(index + 1):
            curr = curr.next
        return curr.value

    def add_at_head(self, value):
        """在头结点前添加结点"""
        self.add_at_index(0, value)

    def add_at_tail(self, value):
        """在尾结点之后添加结点"""
        self.add_at_index(self._size, value)

    def add_at_index(self, index: int, value):
        """在指定座标前添加结点(若座标无效则不添加)"""
        if index < 0 or index > self._size:
            return
        self._size += 1
        prev = self._head
        for _ in range(index):
            prev = prev.next
        node = self._Node(value, prev.next)
        prev.next = node

    def delete_at_index(self, index: int):
        """依据座标删除结点(若座标无效则不删除)"""
        if index < 0 or index >= self._size:
            return
        self._size -= 1
        prev = self._head
        for _ in range(index):
            prev = prev.next
        prev.next = prev.next.next