Syntax error Program to find union of two given linked lists in Python

Program to find union of two given linked lists in Python

Suppose we have two sorted linked lists L1 and L2, we have to return a new sorted linked list that is the union of the two given lists.

So, if the input is like L1 = [10,20,30,40,50,60,70] L2 = [10,30,50,80,90], then the output will be [10, 20, 30, 40, 50, 60, 70, 80, 90, ]

To solve this, we will follow these steps −

  • Define a function solve() . This will take L1, L2
  • if L1 is empty, then
    • return L2
  • if L2 is empty, then
    • return L1
  • if value of L1 < value of L2, then
    • res := L1
    • next of res := solve(next of L1, L2)
  • otherwise when value of L2 < value of L1, then
    • res := L2
    • next of res := solve(next of L2, L1)
  • otherwise,
    • res := L1
    • next of res := solve(next of L1, next of L2)
  • return res

Let us see the following implementation to get better understanding −

Example

 Live Demo

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):
      if not L1:
         return L2
      if not L2:
         return L1
      if L1.val < L2.val:
         res = L1
         res.next = self.solve(L1.next, L2)
      elif L2.val < L1.val:
         res = L2
         res.next = self.solve(L2.next, L1)
      else:
         res = L1
         res.next = self.solve(L1.next, L2.next)
   return res
ob = Solution()
L1 = make_list([10,20,30,40,50,60,70])
L2 = make_list([10,30,50,80,90])
print_list(ob.solve(L1, L2))

Input

[10,20,30,40,50,60,70], [10,30,50,80,90]

Output

[10, 20, 30, 40, 50, 60, 70, 80, 90, ]
Updated on: 2020-11-19T07:08:44+05:30

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