83-remove-duplicates-from-sorted-list.py

# 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]:
        dummy = prev = ListNode(val= float('-inf'), next=head)
        cur = head
        while cur:
            if prev.val == cur.val:
                prev.next = None
                cur = cur.next
            else:
                prev.next = cur
                prev = cur
                cur = cur.next
        return dummy.next
    
# time O(n)
# space O(1)
# using linked list and two pointers (prev and cur)