Remove Duplicates from Sorted List 

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


For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->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 visited=head;
        while(visited!=null&&visited.next!=null){
            if(visited.val==visited.next.val)
                visited.next=visited.next.next;
            else
               visited=visited.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.
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 pre=new ListNode(0);
		pre.next=head;
		head=pre;		
		while(pre.next!=null){
			ListNode cur=pre.next;
			while(cur.next!=null&&cur.next.val==cur.val)
				cur=cur.next;
			if(pre.next==cur){ // don't find the duplicate
				pre=pre.next;
			}else{ //remove the duplicate node
				pre.next=cur.next;
			}
		}
		return head.next;
    }
}

LeetCode Solutions : Remove Duplicates from Sorted List I & II