## Remove Duplicates from Sorted List I

Given a sorted linked list, delete all duplicates such that each element appear only *once.*

**Example**

Given `1->1->2`

, return `1->2`

.

Given `1->1->2->3->3`

, return `1->2->3`

.

public static ListNode deleteDuplicates(ListNode head) { if (head == null || head.next == null) { return head; } ListNode runner = head; while (runner.next != null) { if (runner.next.val == runner.val) { runner.next = runner.next.next; } else { runner = runner.next; } } return head; }

## Remove Duplicates from Sorted List II

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

**Example**

Given `1->2->3->3->4->4->5`

, return `1->2->5`

.

Given `1->1->1->2->3`

, return `2->3`

.

public static ListNode deleteDuplicates(ListNode head) { if(head==null||head.next==null){ return head; } ListNode dummyHead = new ListNode(-1); dummyHead.next = head; ListNode runner = dummyHead; int preValue = dummyHead.val; while(runner.next!=null){ if(runner.next.val==preValue || (runner.next.next!=null && runner.next.next.val == runner.next.val)){ preValue = runner.next.val;//keep track of the previous value runner.next = runner.next.next;//delete runner.next }else{ preValue = runner.next.val; runner = runner.next;//keep moving forward } } return dummyHead.next; }