10，单链表

链表简介

链表是一种特殊的数据结构，它的优点是储存数据时不需要连续的内存空间（可以利用分散的空间），缺点是时间复杂度和空间复杂度较高。

单链表代码实现

单链表只能单向前进，用python语言实现它的代码如下：

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

class SingleLinkList(object):
    def __init__(self, node=None):
        self.__head = node

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

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

    def travel(self):
        cur = self.__head
        while cur != None:
            print(cur.elem)
            cur = cur.next

    def add(self, item):
        node = Node(item)
        node.next = self.__head
        self.__head = node

    def append(self, item):
        node = Node(item)
        if self.is_empty():
            self.__head = node
        else:
            cur = self.__head
            while cur.next != None:
                cur = cur.next
            cur.next = node

    def insert(self, pos, item):
        if pos <= 0:
            self.add(item)
        elif pos > (self.length()-1):
            self.append(item)
        else:
            node = Node(item)
            pre = self.__head
            count = 0
            while count < (pos-1):
                pre = pre.next
                count += 1
            node.next = pre.next
            pre.next = node

    def remove(self, item):
        cur = self.__head
        pre = self.__head
        while cur != None:
            if cur.elem == item:
                if pre == None:
                    self.__head = cur.next
                else:
                    pre.next = cur.next
            else:
                pre = cur
                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