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:

首先用hashmap计算每个元素出现的次数，然后给list加个头指针，然后遍历链表，将次数多于1的都删掉。

 

 1 /**

 2  * Definition for singly-linked list.

 3  * public class ListNode {

 4  *     int val;

 5  *     ListNode next;

 6  *     ListNode(int x) {

 7  *         val = x;

 8  *         next = null;

 9  *     }

10  * }

11  */

12 public class Solution {

13     public ListNode deleteDuplicates(ListNode head) {

14         // Start typing your Java solution below

15         // DO NOT write main() function

16         HashMap<Integer,Integer> map = new HashMap<Integer,Integer>();

17         ListNode cur = head;

18         while(cur != null){

19             if(map.containsKey(cur.val)){

20                 map.put(cur.val,map.get(cur.val) + 1);

21             }else{

22                 map.put(cur.val,1);

23             }

24             cur = cur.next;

25         }

26         ListNode header = new ListNode(-1);

27         header.next = head;

28         cur = header;

29         while(cur.next != null){

30             if(map.get(cur.next.val) > 1){

31                 cur.next = cur.next.next;

32             }

33             else{

34                 cur = cur.next;

35             }

36         }

37         return header.next;

38     }

39 }