Question

Given a sorted linked list, delete all duplicates such that each element appear only once.

Example 1:

Input: 1->1->2
Output: 1->2

Example 2:

Input: 1->1->2->3->3
Output: 1->2->3

Thinking:

  • Method 1:
    • 循环。
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if(head == null) return head;
        ListNode dummy = new ListNode(Integer.MIN_VALUE);
        dummy.next = head;
        ListNode cur = dummy;
        ListNode pre = dummy;
        while(cur.next != null){
            if(cur.next.val != pre.val){
                pre.next = cur.next;
                pre = pre.next;
                cur = cur.next;
            }else{
                cur = cur.next;
            }
        }
        pre.next = null;
        return dummy.next;
    }
}

二刷

这道题二刷的时候还是很顺利的，很快就出结果了。

/**
 * 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 cur = dummy.next;
        ListNode pre = dummy;
        while(cur != null && cur.next != null){
            while(cur.next != null && cur.val == cur.next.val){
                cur = cur.next;
            }
            pre.next = cur;
            cur = cur.next;
            pre = pre.next;
        }
        return dummy.next;
    }
}

Reference

  1. Remove Duplicates from Sorted List II