code-5.java

/**
 * 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 iter = head;
        head=null;
        ListNode distinctNode = null;
        ListNode prev = iter;
        boolean prevIsDu = false;//prev node is duplicate
        iter = iter.next;
        while(iter!=null){
            if(iter.val!=prev.val){
                if(prevIsDu)
                    prevIsDu=false;
                else if(distinctNode==null){
                    distinctNode=prev;
                    head=distinctNode;
                }
                else{
                    distinctNode.next=prev;
                    distinctNode=distinctNode.next;
                }
                prev=iter;
            }
            else    prevIsDu=true;
            iter=iter.next;
        }
        if(!prevIsDu) {
            if(distinctNode==null){
                distinctNode=prev;
                head=distinctNode;
            }
            else{
                distinctNode.next=prev;
                distinctNode=distinctNode.next;
            }
        }
        if(distinctNode!=null)
            distinctNode.next=null;
        return head;
    }
}