Interleave List Elements from Two Linked Lists in Python

Suppose we have two linked lists l1 and l2, we have to return one linked list by interleaving elements of these two lists starting with l1. If there are any leftover nodes in a linked list, they should be appended to the list.

So, if the input is like l1 = [5,4,6,3,4,7] l2 = [8,6,9], then the output will be [5,8,4,6,6,9,3,4,7]

To solve this, we will follow these steps −

• ans := l1

• while l2 is not null, do

  • if ans is not null, then

    • if next of ans is not null, then

      • newnode := a new list node with same value of l2

      • next of newnode := next of ans

      • next of ans := newnode

      • ans := next of newnode

      • l2 := next of l2

    • otherwise,

    • next of ans := l2

    • come out from the loop

  • otherwise,

    
    

    • return l2

      
      

• return l1

Let us see the following implementation to get better understanding −

Example

Source Code (Python):
class ListNode:
   def __init__(self, data, next = None):
      self.val = data
      self.next = next

def make_list(elements):
   head = ListNode(elements[0])
   for element in elements[1:]:
      ptr = head
      while ptr.next:
         ptr = ptr.next
      ptr.next = ListNode(element)

   return head

def print_list(head):
   ptr = head
   print('[', end = "")
   while ptr:
      print(ptr.val, end = ", ")
      ptr = ptr.next
print(']')

class Solution:
   def solve(self, l1, l2):
      ans = l1
      while l2:
         if ans:
            if ans.next != None:
               newnode = ListNode(l2.val, None)
               newnode.next = ans.next
               ans.next = newnode
               ans = newnode.next
               l2 = l2.next
            else:
               ans.next = l2
               break
            else:
               return l2
               return l1

ob = Solution()
l1 = make_list([5,4,6,3,4,7])
l2 = make_list([8,6,9])
res = ob.solve(l1,l2)
print_list(res)

Input

[5,4,6,3,4,7],[8,6,9]

Output

[5, 8, 4, 6, 6, 9, 3, 4, 7, ]