0082-remove-duplicates-from-sorted-list-ii.rb

# frozen_string_literal: true

# 82. Remove Duplicates from Sorted List II
# https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii
# Medium

=begin
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]

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.
=end

# Definition for singly-linked list.
# class ListNode
#     attr_accessor :val, :next
#     def initialize(val = 0, _next = nil)
#         @val = val
#         @next = _next
#     end
# end
# @param {ListNode} head
# @return {ListNode}
def delete_duplicates(head)
  dummy = ListNode.new(-101, head)
  prev = dummy
  current = head

  while current
    if current.next && current.val == current.next.val
      while current.next && current.val == current.next.val
        current = current.next
      end
      prev.next = current.next
    else
      prev = current
    end
    current = current.next
  end

  dummy.next
end