Remove Duplicates from Sorted List II (Java)

LeetCode

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

For example,
Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 2->3.

Solution: 

The logic is pretty straight, however, the corner cases need pay more attention.
check the comments in the code.

	/*
	Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.
	For example,
	Given 1->2->3->3->4->4->5, return 1->2->5.
	Given 1->1->1->2->3, return 2->3.
	*/
	/**
	* Definition for singly-linked list.
	* public class ListNode {
	* int val;
	* ListNode next;
	* ListNode(int x) {
	* val = x;
	* next = null;
	* }
	* }
	*/
	public class Solution {
	public ListNode deleteDuplicates(ListNode head) {
	if (head==null || head.next==null){
	return head;
	}
	ListNode preHead=new ListNode (-1);
	preHead.next=head;
	ListNode pre=preHead;
	ListNode current=head;
	ListNode run=current.next;
	while (current!=null && run!=null){
	// check duplicats for current node;
	while (run!=null && run.val==current.val){
	run=run.next;
	}
	if (run==null){
	// current next is run, so no duplicate need to be removed
	// and no more nodes need to be check
	if (current.next==null){
	return preHead;
	}
	else{
	// current node until to null are all repeated
	// should remove them all.
	pre.next=null;
	return preHead.next;
	}
	}
	else{
	if (current.next==run){
	// no duplicate
	pre=current;
	current=run;
	run=run.next;
	}
	else{
	// removed duplicate
	pre.next=run;
	current=run;
	run=current.next;
	}
	}
	}
	return preHead.next;
	}
	}

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