82. Remove Duplicates from Sorted List II

82. Remove Duplicates from Sorted List II

Given the head of a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list. Return the linked list sorted as well.

Example 1:

Input: head = [1,2,3,3,4,4,5]
Output: [1,2,5]

Example 2:

Input: head = [1,1,1,2,3]
Output: [2,3]


  • The number of nodes in the list is in the range [0, 300].
  • -100 <= Node.val <= 100
  • The list is guaranteed to be sorted in ascending order.



  • Idea

    • Base case: list is empty or contains only one element –> No duplicates
    • Recursive case: Assuming that the rest of the list is already done removing duplicates, we only need to consider the first part
      • There’s no duplicate in the first part
      • There’re duplicates in the first part
# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def deleteDuplicates(self, head: Optional[ListNode]) -> Optional[ListNode]:
        if not head or not head.next:
            return head
        if head.val != head.next.val:
            head.next = self.deleteDuplicates(head.next)
            return head
        current = head
        while current.next and current.next.val == current.val:
            current = current.next
        return self.deleteDuplicates(current.next)
No Comments

Post A Comment

7 + fifteen =