82. Remove Duplicates from Sorted List II

Problem:

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.

Analysis:

Since it needs to remove all dup, so we need to have a pre pointer comparing to 82.

Solution:

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode p = dummy;
        while (p.next != null && p.next.next != null) {
            if (p.next.val == p.next.next.val) {
                int dup = p.next.val;
                while (p.next != null && p.next.val == dup) {
                    p.next = p.next.next;
                }
            } else {
                p = p.next;
            }
        }
        return dummy.next;
    }
}