Creating a linked list with digits of a given number-CodePudding

I'm currently self studying some programming and I have stumbled upon a problem that asks you to make a linked list which contains digits of a certain number (from last to first). This is the code that I wrote and i have no idea why it does't work. I've created simple node class and a Number class that will hold my list.

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

    def __str__(self):
        return str(self.val)


class Number:
    def __init__(self):
        self.first = None

    def set(self, num):
        for i in range(len(str(num))):
            tail = Node(num % 10)
            if i == 0:
                head = tail
            num //= 10
            tail = tail.next
        self.first = head

Set function is ment to create a list with given digits, so

n = Number()
n.set(123)

should create a list 3 -> 2 -> 1, but when i try to print it using

def node_printer(head: Node):
    while head is not None:
        if head.next is not None:
            print(str(head)   ", ", end="")
        else:
            print(head)
        head = head.next

and calling node_printer(n.first) I get 3 as an output.

CodePudding user response：

At tail = tail.next since tail was just created, tail.next is None so nothing gets linked.

def set(self, num):
    head = tail = None
    while num:
        # Create new node
        temp = Node(num % 10)
        # Empty list?
        if head == None:
            head = tail = temp
        # Not empty list, append to tail
        else:
            tail.next = temp
        # Update tail for next time
        tail = temp
        num //= 10
    self.first = head

CodePudding user response：

You could approach this by adding to the head rather than tail. It is much easier to get digits of a number that way too:

def numberList(number):
    head = Node(0)                         # initial head of zero
    while number:  
       number,digit = divmod(number,10)    # extract last digit
       newHead = Node(digit)               # make it a node
       newHead.next, head = head, newHead  # link it as newHead
    return head.next or head               # single zero or first digit

You can make this even shorter by adding a nextNode optional parameter to your Node class:

class Node:
    def __init__(self, x=None, nextNode=None):
        self.val  = x
        self.next = nextNode

def numberList(number):
    head = Node(0)                         # initial head of zero
    while number:  
       number,digit = divmod(number,10)    # extract last digit
       head = Node(digit,head)             # make it a node, link old head
    return head.next or head               # single zero or first digit