83. Remove Duplicates from Sorted List

EazyLeetCode

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]

Constraints:

• 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

How to solve the problem

Code

# 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]:
        cur = head
        if cur is None:
            return head
        while cur.next: # when the last node is not None
            if cur.val == cur.next.val:
                cur.next = cur.next.next
            else:
                cur = cur.next # cur++
        return head

Complexity

• Time complexity: O(n)
• Space complexity: O(1)