[LeetCode] 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.

[Solution].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) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(head == null) return null;
        ListNode result = null;
        ListNode begin = null;
        while(head != null){
            int num = head.val;
            if(head.next != null && head.next.val == num){
                while(head != null && head.val == num) head = head.next;
            }
            else{
                if(result == null){
                    result = head;
                    begin = result;
                }
                else{
                    result.next = head;
                    result = result.next;
                }
                head = head.next;
                result.next = null;
            }
        }
        return begin;
        
    }
}