数据结构与算法-链表之双向链表

双向链表

一种更复杂的链表是“双向链表”或“双面链表”。每个节点有两个链接：一个指向前一个节点，当此节点为第一个节点时，指向空值；而另一个指向下一个节点，当此节点为最后一个节点时，指向空值。

实现：

class Node(object):
    """节点"""
    def __init__(self, elem):
        self.elem = elem
        self.prev = None
        self.next = None

class SingleLinkList(object):
    """单向链表"""
    def __init__(self, node=None):
        self.__head = node

    def is_empty(self):
        return self.__head == None

    def length(self):
        """链表长度"""
        cur = self.__head
        count = 0
        while cur != None:
            count += 1
            cur = cur.next
        return count

    def travel(self):
        """遍历整个链表"""
        cur = self.__head
        while cur != None:
            print(cur.elem, end=" ")
            cur = cur.next
        print("")

    def add(self, item):
        """链表头部添加元素"""
        node = Node(item)
        node.next = self.__head
        self.__head = node
        node.next.prev = node # 也可以等于self.head

    def append(self, item):
        """链表尾部添加元素"""
        node = Node(item)
        if self.is_empty():
            self.__head = node
        else:
            cur = self.__head
            while cur.next != None:
                cur = cur.next
            cur.next = node
            node.prev = cur

    def insert(self, pos, item):
        """
        指定位置添加元素
        :param pos: pos 从哪里开始
        :param item:
        :return:
        """
        if pos <= 0:
            self.add(item)
        elif pos > (self.length()-1):
            self.append(item)
        else:
            cur = self.__head
            count = 0
            while count < (pos-1):
                count += 1
                cur = cur.next

            # 当循环退出后，cur指向pos-1的位置
            node = Node(item)
            node.next = cur
            node.prev = cur.prev
            cur.prev.next = node
            cur.prev = node


    def remove(self, item):
        """删除节点"""
        cur = self.__head
        while cur != None:
            if cur.elem == item:
                # 判断是否为头节点
                if cur == self.__head:
                    self.__head = cur.next
                    if cur.next:
                        cur.next.prev = None
                else:
                    cur.prev.next = cur.next #
                    if cur.next:
                        cur.next.prev = cur.prev
                break
            else:
                cur =cur.next

    def search(self, item):
        cur = self.__head
        while cur != None:
            if cur.elem == item:
                return True
            else:
                cur = cur.next
        return False

if __name__ == '__main__':
    ll = SingleLinkList()
    # print(ll.is_empty())
    # print(ll.length())

    ll.append(1)
    print(ll.is_empty())
    print(ll.length())
    ll.append(2)
    ll.add(8)
    ll.append(3)
    ll.append(4)
    ll.append(5)
    ll.append(6)

    ll.travel()
    ll.insert(-1, 9)  # 9 8 1 23456
    ll.travel()
    ll.insert(3, 100)  # 9 8 1 100 2 3456
    ll.travel()
    ll.insert(10, 200)  # 9 8 1 100 23456 200
    ll.travel()
    ll.remove(100)
    ll.travel()
    ll.remove(9)
    ll.travel()
    ll.remove(200)
    ll.travel()
    print(ll.search(77))