CODEWITHSUNDEEP
pythonpython-3.x
Cloud
Cloud

Reputation: 399

Creation of a Linked List

I am trying to created a linked list. However, the following code keeps printing only the last element of the list. Is there an error in my code? I think the problem lies in the "insert" method. I am not able to figure out why though. 

import sys
import io


string = """4
2
3
4
1"""
sys.stdin = io.StringIO(string)


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


class Solution:
    def display(self, head):
        current = head
        while current:
            print(current.data, end=' ')
            current = current.next

    # TODO: Code only prints the last element of data
    def insert(self, head, data):
        if head == None:
            head = Node(data)
            return head
        else:
            head.next = Node(data)
            return head.next


mylist = Solution()
T = int(input())
head = None
for i in range(T):
    data = int(input())
    head = mylist.insert(head, data)

mylist.display(head)

Upvotes: 0

Views: 109

Answers (2)

Mr. E
Mr. E

Reputation: 2130

The problem is you're losing the reference to the head of the list. You must keep the head and insert the new item at the end of the list

def insert(self,head,data): 
    if head == None:
        head = Node(data)
    else:
        current = head
        while current.next != None:
            current = current.next
        current.next = Node(data)
    return head

Upvotes: 4

Martijn Pieters
Martijn Pieters

Reputation: 1124718

You only keep a reference to the end of the chain (head.next), so yes, you'll only be able to display that last element.

You'll need to keep a reference to the first element (the real head):

mylist = Solution()
T = int(input())
current = head = None
for i in range(T):
    data = int(input())
    current = mylist.insert(head, data)
    if head is None:
        head = current

Upvotes: 1

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