Python, how to invert a chained list?

Question

Hello, I need to create a function that receives an unordered list in the structure of nodes and it should reverse the order of the elements of that list, I tried to make a L[::-1] to reverse the list but it didn’t work, I tried hard and I have no idea how to do it, I would like your help. I already have the classes implemented, follows:

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

    def getData(self):
        return self.data

    def getNext(self):
        return self.next

    def setData(self,newdata):
        self.data = newdata

    def setNext(self,newnext):
        self.next = newnext


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

    def __str__(self):
        tmp = self.head
        lstr = ''
        while tmp != None:
            lstr += str(tmp.data) + ' '
            tmp = tmp.getNext()
        
        return lstr

    def isEmpty(self):
        return self.head == None

    def add(self,item):
        temp = Node(item)
        temp.setNext(self.head)
        self.head = temp

    def size(self):
        current = self.head
        count = 0
        while current != None:
            count = count + 1
            current = current.getNext()

        return count

    def search(self,item):
        current = self.head
        found = False
        while current != None and not found:
            if current.getData() == item:
                found = True
            else:
                current = current.getNext()

        return found

    def remove(self,item):
        current = self.head
        previous = None
        found = False
        while not found:
            if current.getData() == item:
                found = True
            else:
                previous = current
                current = current.getNext()

        if previous == None:
            self.head = current.getNext()
        else:
            previous.setNext(current.getNext())

the function to invert the list looks like this:

def inverterLista(L : UnorderedList):
    # solução
    return L

Here some tests:

L = UnorderedList()
L.add(1)
L.add(2)
L.add(3)
L.add(4)
L.add(5)
print(f'Lista antes: {L}')
L = inverterLista(L)
print(f'Lista depois: {L}')

I ask for your help, I’m a beginner in python and I haven’t seen anything like this yet, I haven’t found anything about how to do this in python either, so how could I reverse this chained list?

Answer 1

I added a new function called inverter() in the Unorderedlist class, thus leaving the new class:

class UnorderedList:

def __init__(self):
    self.head = None
    self.lstr=None


def __str__(self):
    tmp = self.head
    self.lstr = ''
    while tmp != None:
        self.lstr += str(tmp.data) + ' '
        tmp = tmp.getNext()

    return self.lstr

def isEmpty(self):
    return self.head == None

def add(self, item):
    temp = Node(item)
    temp.setNext(self.head)
    self.head = temp

def size(self):
    current = self.head
    count = 0
    while current != None:
        count = count + 1
        current = current.getNext()

    return count
def inverter(self):
    v = self.lstr
    tam = len(v)
    l_inv = ''

    while tam >= 0:
        l_inv += v[tam - 1]
        tam -= 1


    return l_inv


def search(self, item):
    current = self.head
    found = False
    while current != None and not found:
        if current.getData() == item:
            found = True
        else:
            current = current.getNext()

    return found

def remove(self, item):
    current = self.head
    previous = None
    found = False
    while not found:
        if current.getData() == item:
            found = True
        else:
            previous = current
            current = current.getNext()

    if previous == None:
        self.head = current.getNext()
    else:
        previous.setNext(current.getNext())

After that if we test this way below it works:

L = UnorderedList()
L.add(1)
L.add(2)
L.add(3)
L.add(4)
L.add(5)


print(f'Lista antes: {L}')
print(f'Lista depois: {L.inverter()}')