剑指offer_删除链表中重复的结点

在一个排序的链表中，存在重复的结点，请删除该链表中重复的结点，重复的结点不保留，返回链表头指针。 例如，链表1->2->3->3->4->4->5 处理后为 1->2->5

首先想到的是先查出哪些元素的值是重复的丢到set里面，然后遍历删除。

/*
 public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}
*/
import java.util.HashSet;
import java.util.Set;
public class Solution {
    public ListNode deleteDuplication(ListNode pHead)
    {    
        if(pHead == null) return null;
         Set<Integer> set = new HashSet<Integer>();
         ListNode cur = pHead;
         while(cur.next!=null) {
             if(cur.val == cur.next.val) set.add(cur.val);
             cur = cur.next;
         }
        cur = pHead;
        while(cur.next!=null) {
             if(set.contains(cur.val)) 
             {pHead = deleteNode(pHead,cur);}
            else{
             cur = cur.next;
            }
        }
     if(set.contains(cur.val)) 
             {pHead = deleteNode(pHead,cur);}
         return pHead;
    }
    
    
    public ListNode deleteNode(ListNode head ,ListNode tobeDelete)
    {
    if(head==null||tobeDelete==null) return null;
    if(tobeDelete.next!=null)
    {
        ListNode next = tobeDelete.next;
        tobeDelete.val =next.val;
        tobeDelete.next=next.next;
    }
    else
    {
        if(head==tobeDelete)
            head=null;
        else
        {
            ListNode cur = head;
            while(cur.next!=tobeDelete)
                cur=cur.next;
            cur.next=null;
        }    
    }
            return head;
    }
}

另外可以递归删除

public ListNode deleteDuplication(ListNode pHead){
    if(pHead == null||pHead.next==null) 
        return pHead;
    ListNode next = pHead.next;
    if(pHead.val=next.val)
        {
            while(next!=null&&pHead.val==next.val){
            next=next.next;
        }
        return deleteDuplication(next);
    }
    else{
        pHead.next=deleteDuplication(pHead.next);
        return pHead;
    }
}