Remove Duplicates from Sorted List II 解答

Question

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

Note here we need to consider head of the list. For example, for input 1 -> 1, we need to return null.

 /**
  * Definition for singly-linked list.
  * public class ListNode {
  *     int val;
  *     ListNode next;
  *     ListNode(int x) { val = x; }
  * }
  */
 public class Solution {
     public ListNode deleteDuplicates(ListNode head) {
         if (head == null || head.next == null)
             return head;
         while (head.next != null && head.val == head.next.val) {
             while (head.next != null && head.val == head.next.val)
                 head = head.next;
             if (head.next != null)
                 head = head.next;
             else
                 return null;
         }
         ListNode current = head, next1, next2;
         while (current != null && current.next != null && current.next.next != null) {
             next1 = current.next;
             next2 = current.next.next;
             if (next1.val != next2.val) {
                 current = current.next;
             } else {
                 while (next2 != null && next1.val == next2.val)
                     next2 = next2.next;
                 current.next = next2;
             }
         }
         return head;
     }
 }