LeetCode 83. Remove Duplicates from Sorted List



Given the head of a sorted linked list, delete all duplicates such that each element appears only once. Return the linked list sorted as well.

Example 1:

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

Example 2:

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


  • 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.


Have a dictionary to track the visited node values.

Python Solution

# 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: ListNode) -> ListNode:
        dummy = ListNode(0)
        dummy.next = head
        visited = set()
        while head and head.next:
            while head.next and head.next.val in visited:
                head.next = head.next.next
            head = head.next
        return dummy.next
  • Time Complexity: O(N).
  • Space Complexity: O(N).

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