鏈表是一系列數(shù)據(jù)元素，通過(guò)鏈接連接在一起。每個(gè)數(shù)據(jù)元素都以指針的形式包含到另一個(gè)數(shù)據(jù)元素的連接。 Python在其標(biāo)準(zhǔn)庫(kù)中沒(méi)有鏈接列表。我們使用前一章討論的節(jié)點(diǎn)概念來(lái)實(shí)現(xiàn)鏈表的概念。我們已經(jīng)知道如何創(chuàng)建節(jié)點(diǎn)類(lèi)以及如何遍歷節(jié)點(diǎn)的元素。在本章中，將學(xué)習(xí)鏈表的類(lèi)型:單鏈表。在這種類(lèi)型的數(shù)據(jù)結(jié)構(gòu)中，任何兩個(gè)數(shù)據(jù)元素之間只有一個(gè)鏈接。創(chuàng)建一個(gè)鏈表并使用一些方法來(lái)插入，更新和從列表中移除元素。

創(chuàng)建鏈表

通過(guò)使用在上一章中學(xué)習(xí)的節(jié)點(diǎn)類(lèi)來(lái)創(chuàng)建鏈表。創(chuàng)建一個(gè)Node對(duì)象并創(chuàng)建另一個(gè)類(lèi)來(lái)使用這個(gè)節(jié)點(diǎn)對(duì)象。通過(guò)節(jié)點(diǎn)對(duì)象傳遞適當(dāng)?shù)闹祦?lái)指向下一個(gè)數(shù)據(jù)元素。下面的程序使用三個(gè)數(shù)據(jù)元素創(chuàng)建鏈接列表。在下一節(jié)中，將學(xué)習(xí)如何遍歷鏈表。

class Node:
    def __init__(self, dataval=None):
        self.dataval = dataval
        self.nextval = None

class SLinkedList:
    def __init__(self):
        self.headval = None

list1 = SLinkedList()
list1.headval = Node("Mon")
e2 = Node("Tue")
e3 = Node("Wed")
# Link first Node to second node
list1.headval.nextval = e2

# Link second Node to third node
e2.nextval = e3

遍歷鏈表

從第一個(gè)數(shù)據(jù)元素開(kāi)始，單向鏈表只能在向前遍歷。只需通過(guò)將下一個(gè)節(jié)點(diǎn)的指針指向當(dāng)前數(shù)據(jù)元素來(lái)打印下一個(gè)數(shù)據(jù)元素的值。

class Node:
    def __init__(self, dataval=None):
        self.dataval = dataval
        self.nextval = None

class SLinkedList:
    def __init__(self):
        self.headval = None

    def listprint(self):
        printval = self.headval
        while printval is not None:
            print (printval.dataval)
            printval = printval.nextval

list = SLinkedList()
list.headval = Node("Mon")
e2 = Node("Tue")
e3 = Node("Wed")

# Link first Node to second node
list.headval.nextval = e2

# Link second Node to third node
e2.nextval = e3

list.listprint()

執(zhí)行上面示例代碼，得到以下結(jié)果 -

Mon
Tue
Wed

向鏈表插入數(shù)據(jù)

在鏈表中插入元素涉及將指針從現(xiàn)有節(jié)點(diǎn)重新分配給新插入的節(jié)點(diǎn)。取決于新數(shù)據(jù)元素是在鏈表的開(kāi)始位置還是在中間位置或末尾插入，有以下解決方案。

在鏈接列表的開(kāi)頭插入

這涉及到將新數(shù)據(jù)節(jié)點(diǎn)的下一個(gè)指針指向鏈表的當(dāng)前頭部。因此，鏈表的當(dāng)前頭成為第二個(gè)數(shù)據(jù)元素，新節(jié)點(diǎn)成為鏈表的頭部。

class Node:
    def __init__(self, dataval=None):
        self.dataval = dataval
        self.nextval = None

class SLinkedList:
    def __init__(self):
        self.headval = None

# Print the linked list
    def listprint(self):
        printval = self.headval
        while printval is not None:
            print (printval.dataval)
            printval = printval.nextval
    def AtBegining(self,newdata):
        NewNode = Node(newdata)

# Update the new nodes next val to existing node
        NewNode.nextval = self.headval
        self.headval = NewNode

list = SLinkedList()
list.headval = Node("Mon")
e2 = Node("Tue")
e3 = Node("Wed")

list.headval.nextval = e2
e2.nextval = e3

list.AtBegining("Sun")

list.listprint()

執(zhí)行上面示例代碼，得到以下結(jié)果 -

Sun
Mon
Tue
Wed

在鏈表的末尾插入

這包括將鏈表的當(dāng)前最后一個(gè)節(jié)點(diǎn)的下一個(gè)指針指向新的數(shù)據(jù)節(jié)點(diǎn)。因此鏈表的當(dāng)前最后一個(gè)節(jié)點(diǎn)成為倒數(shù)第二個(gè)數(shù)據(jù)節(jié)點(diǎn)，新節(jié)點(diǎn)成為鏈表的最后一個(gè)節(jié)點(diǎn)。參考以下代碼實(shí)現(xiàn) -

class Node:
    def __init__(self, dataval=None):
        self.dataval = dataval
        self.nextval = None

class SLinkedList:
    def __init__(self):
        self.headval = None

# Function to add newnode
    def AtEnd(self, newdata):
        NewNode = Node(newdata)
        if self.headval is None:
            self.headval = NewNode
            return
        laste = self.headval
        while(laste.nextval):
            laste = laste.nextval
        laste.nextval=NewNode

# Print the linked list
    def listprint(self):
        printval = self.headval
        while printval is not None:
            print (printval.dataval)
            printval = printval.nextval


list = SLinkedList()
list.headval = Node("Mon")
e2 = Node("Tue")
e3 = Node("Wed")

list.headval.nextval = e2
e2.nextval = e3

list.AtEnd("Thu")

list.listprint()

執(zhí)行上面代碼，得到以下結(jié)果 -

Mon
Tue
Wed
Thu

在兩個(gè)數(shù)據(jù)節(jié)點(diǎn)之間插入

這涉及到將指定節(jié)點(diǎn)的指針指向新節(jié)點(diǎn)。這可以通過(guò)傳入新節(jié)點(diǎn)和現(xiàn)有節(jié)點(diǎn)，然后插入新節(jié)點(diǎn)。所以定義一個(gè)額外的類(lèi)，將新節(jié)點(diǎn)的下一個(gè)指針改變?yōu)橹虚g節(jié)點(diǎn)的下一個(gè)指針。然后將新節(jié)點(diǎn)分配給中間節(jié)點(diǎn)的下一個(gè)指針。參考以下代碼實(shí)現(xiàn) -

class Node:
    def __init__(self, dataval=None):
        self.dataval = dataval
        self.nextval = None

class SLinkedList:
    def __init__(self):
        self.headval = None

# Function to add node
    def Inbetween(self,middle_node,newdata):
        if middle_node is None:
            print("The mentioned node is absent")
            return

        NewNode = Node(newdata)
        NewNode.nextval = middle_node.nextval
        middle_node.nextval = NewNode

# Print the linked list
    def listprint(self):
        printval = self.headval
        while printval is not None:
            print (printval.dataval)
            printval = printval.nextval


list = SLinkedList()
list.headval = Node("Mon")
e2 = Node("Tue")
e3 = Node("Thu")

list.headval.nextval = e2
e2.nextval = e3

list.Inbetween(list.headval.nextval,"Fri")

list.listprint()

執(zhí)行上面示例代碼，得到以下結(jié)果 -

Mon
Tue
Fri
Thu

從鏈表中刪除項(xiàng)目

可以使用該節(jié)點(diǎn)的鍵來(lái)刪除一個(gè)節(jié)點(diǎn)。在下面的程序中，找到要?jiǎng)h除的節(jié)點(diǎn)的前一個(gè)節(jié)點(diǎn)。然后將該節(jié)點(diǎn)的下一個(gè)指針指向要?jiǎng)h除的節(jié)點(diǎn)的下一個(gè)節(jié)點(diǎn)。

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

class SLinkedList:
    def __init__(self):
        self.head = None

    def Atbegining(self, data_in):
        NewNode = Node(data_in)
        NewNode.next = self.head
        self.head = NewNode

# Function to remove node
    def RemoveNode(self, Removekey):

        HeadVal = self.head

        if (HeadVal is not None):
            if (HeadVal.data == Removekey):
                self.head = HeadVal.next
                HeadVal = None
                return

        while (HeadVal is not None):
            if HeadVal.data == Removekey:
                break
            prev = HeadVal
            HeadVal = HeadVal.next

        if (HeadVal == None):
            return

        prev.next = HeadVal.next

        HeadVal = None

    def LListprint(self):
        printval = self.head
        while (printval):
            print(printval.data),
            printval = printval.next


llist = SLinkedList()
llist.Atbegining("Mon")
llist.Atbegining("Tue")
llist.Atbegining("Wed")
llist.Atbegining("Thu")
llist.RemoveNode("Tue")
llist.LListprint()

執(zhí)行上面示例代碼，得到以下結(jié)果 -

Thu
Wed
Mon

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Python鏈表

創(chuàng)建鏈表

遍歷鏈表

向鏈表插入數(shù)據(jù)

從鏈表中刪除項(xiàng)目