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;
    }
}