82 Remove Duplicates from Sorted List II

82. Remove Duplicates from Sorted List II

1. Question

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving onlydistinctnumbers from the original list.

For example, Given1->2->3->3->4->4->5, return1->2->5. Given1->1->1->2->3, return2->3.

2. Implementation

/**
 * 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 preNode = dummy, curNode = head;

        while (curNode != null) {
            while (curNode.next != null && curNode.val == curNode.next.val) {
                curNode = curNode.next;
            } 

            if (preNode.next != curNode) {
                preNode.next = curNode.next;
            }
            else {
                preNode = preNode.next;
            }
            curNode = curNode.next;
        }
        return dummy.next;
    }
}

3. Time & Space Complexity

时间复杂度O(n), 空间复杂度O(1)