Remove Duplicate Entries in a Linked List in Python

Suppose we have a linked list of numbers, we have to remove those numbers which appear multiple times in the linked list (hold only one occurrence in the output), we also have to maintain the order of the appearance in the original linked list.

So, if the input is like [2 -> 4 -> 6 -> 1 -> 4 -> 6 -> 9], then the output will be [2 -> 4 -> 6 -> 1 -> 9].

To solve this, we will follow these steps −

• if node is not null, then
  • l := a new set
  • temp := node
  • insert value of temp into l
  • while next of temp is not null, do
    • if value of next of temp is not in l, then
      • insert value of next of temp into l
      • temp := next of temp
    • otherwise,
      • next of temp := next of next of temp
• return node

Let us see the following implementation to get better understanding −

Example

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, node):
      if node:
         l = set()
         temp = node
         l.add(temp.val)
         while temp.next:
            if temp.next.val not in l: l.add(temp.next.val)
               temp = temp.next
            else:
               temp.next = temp.next.next
         return node
ob = Solution()
head = make_list([2, 4, 6, 1, 4, 6, 9])
print_list(ob.solve(head))

Input

[2, 4, 6, 1, 4, 6, 9]

Output

[2, 4, 6, 1, 9, ]