數據結構 之 '鏈表'

鏈表

鏈表是一種物理存儲單元上非連續、非順序的存儲結構，數據元素的邏輯順序是經過鏈表中的指針連接次序實現的。鏈表由一系列結點（鏈表中每個元素稱爲結點）組成，結點能夠在運行時動態生成。每一個結點包括兩個部分：一個是存儲數據元素的數據域，另外一個是存儲下一個結點地址的指針域。 相比於線性表順序結構，操做複雜。因爲沒必要須按順序存儲，鏈表在插入的時候能夠達到O(1)的複雜度，比另外一種線性表順序錶快得多，可是查找一個節點或者訪問特定編號的節點則須要O(n)的時間，而線性表和順序表相應的時間複雜度分別是O(logn)和O(1)。

基本操做

class Node(object):
    """
    封裝節點
    """
    def __init__(self, item):
        # 存儲數據元素的數據域
        self.item = item

        # 存儲下一個結點地址的指針域
        self.next = None


class Link(object):
    """
    封裝鏈表
    """
    def __init__(self):
        # 初始化一個空鏈表
        self._head = None
        # '_head' 用於指向鏈表的第一個節點

    def add(self, item):
        """
        鏈表首部插入節點
        :param item:
        :return:
        """
        node = Node(item)
        node.next = self._head
        self._head = node

    def travel(self):
        """
        遍歷每個節點
        :return:
        """
        cur = self._head
        while cur:
            print(cur.item)
            cur = cur.next

    def length(self):
        """
        鏈表中節點的個數
        :return:
        """
        count_node = 0
        cur = self._head
        while cur:
            count_node += 1
            cur = cur.next
        return count_node

    def isEmpty(self):
        """
        判斷鏈表是否爲空
        :return:
        """
        return self._head == None

    def search(self, item):
        """
        查找是否存在item對應的節點
        :param item:
        :return:
        """
        find = False
        cur = self._head
        while cur:
            if cur.item == item:
                find = True
                break
            else:
                cur = cur.next
        return find

    def append(self, item):
        """
        鏈表的尾部插入節點
        :param item:
        :return:
        """
        node = Node(item)
        if self._head == None:
            self._head = node
            return

        cur = self._head
        pre = None
        while cur:
            pre = cur
            cur = cur.next
        pre.next = node

    def insert(self, pos, item):
        """
        鏈表中指定的位置插入新的節點
        :param pos:
        :param item:
        :return:
        """
        node = Node(item)
        if pos == 0:
            node.next = self._head
            self._head = node
            return
        pre = None
        cur = self._head
        for i in range(pos):
            pre = cur
            cur = cur.next
        pre.next = node
        node.next = cur

    def remove(self, item):
        """
        刪除節點
        :param item: 
        :return: 
        """
        cur = self._head
        pre = None

        if cur.item == item:
            self._head = cur.next
            return
        while True:
            pre = cur
            cur = cur.next
            if cur.item == item:
                pre.next = cur.next
                break
            if cur == None:
                break

    def reverse(self):
        """
        鏈表倒置
        :return: 
        """
        pre = None
        cur = self._head
        next_node = cur.next

        while cur:
            cur.next = pre
            pre = cur
            cur = next_node
            if cur != None:
                next_node = next_node.next
        self._head = pre
        self.travel()


if __name__ == '__main__':
    link = Link()
    link.append(1)
    link.append(2)
    link.append(3)
    link.append(4)
    link.reverse()
    

# 4
# 3
# 2
# 1