CODEWITHSUNDEEP
pythonlinked-list
BWallDev
BWallDev

Reputation: 375

Python Linked List Trouble

I am trying to convert a string of numbers into a linked list of integers. For some reason when I go to print the value of each value in the linked list, it only prints the first value. For example: a string "523" would be turned into a linked list: 5->2->3, but it's only printing the first node value 5. Can someone please help me see what I am missing? Thanks for any help!

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

total = "523"
root = None
curr_node = None

for digit in total:
    if root is None:
        root = ListNode(int(digit), curr_node)
    else:
        curr_node = ListNode(int(digit))
        curr_node = curr_node.next

while root:
    print(root.val)
    root = root.next

Upvotes: 0

Views: 49

Answers (1)

tobias_k
tobias_k

Reputation: 82949

The problem with your code is that assigning a new value to curr_node does not change the None value currently assigned to root.next or curr_node.next. Instead, you should keep a reference to the current/last node itself:

root = last = None
for digit in total:
    if root is None:
        root = last = ListNode(int(digit))
    else:
        last.next = last = ListNode(int(digit))

Alternatively: Creating a recursive data structure like a linked list is often easier and more "natural" using a recursive function instead of a loop:

def to_list(s):
    if s:
        return ListNode(int(s[0]), to_list(s[1:]))
    else:
        return None

root = to_list(total)

Upvotes: 1

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