How to traverse Linked-Lists Python

Question

I am trying to figure out how I can traverse linked list in Python using Recursion.

I know how to traverse linked-lists using common loops such as:

 item_cur = my_linked_list.first
       while item_cur is not None:
           print(item_cur.item)
           item_cur = item_cur.next

I was wondering how I could turn this loop into a recursive step.

Thanks

Recursion is not a desirable solution in python, since you won't be able to go past element 1000 in the list — Eric, Oct 18 '14 at 23:37
@Eric. humm okay.. but when I print the rest .. it gives me a memory address. — Andre, Oct 18 '14 at 23:39
`print the rest` needs to print a linked list. But you've just written a function that knows how to print a linked list. So call that instead of `print` — Eric, Oct 18 '14 at 23:43
the function you are referring to is *item*, I presume. Because item is what reveals the value of the element in the linked list. — Andre, Oct 18 '14 at 23:47

score 6 · Answer 1 · answered Oct 19 '14 at 03:31

6

You could do something like this:

def print_linked_list(item):
    # base case
    if item == None:
        return
    # lets print the current node 
    print(item.item)
    # print the next nodes
    print_linked_list(item.next)

answered Oct 19 '14 at 03:31

avi

9,292
11
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84

score 1 · Answer 2 · edited Feb 06 '20 at 19:47

1

Try this.

class Node:
    def __init__(self,val,nxt):
        self.val = val
        self.nxt = nxt  
def reverse(node):
    if not node.nxt:
        print node.val
        return 
    reverse(node.nxt)
    print node.val

n0 = Node(4,None)
n1 = Node(3,n0)
n2 = Node(2,n1)
n3 = Node(1,n2)

reverse(n3)

edited Feb 06 '20 at 19:47

Vijay

143
1
1
10

answered Oct 19 '14 at 03:15

Kipi

165
2
10

score 0 · Answer 3 · answered Oct 19 '14 at 05:04

It looks like your linked list has two kinds of parts. You have list nodes, with next and item attributes, and a wrapper object which has an attribute pointing to a the first node. To recursively print the list, you'll want to have two functions, one to handle the wrapper and a helper function to do the recursive processing of the nodes.

def print_list(linked_list):               # Non-recursive outer function. You might want
    _print_list_helper(linked_list.first)  # to update it to handle empty lists nicely!

def _print_list_helper(node):              # Recursive helper function, gets passed a
    if node is not None:                   # "node", rather than the list wrapper object.
        print(node.item)
        _print_list_helper(node.next)      # Base case, when None is passed, does nothing

How to traverse Linked-Lists Python

3 Answers3