2.1---删除链表中重复元素（CC150）

分成两种，1种开了额外空间，临时缓冲区，一种没有开

import java.util.HashSet;
import java.util.Set;

class ListNode{
    int data;
    ListNode next;
}

public class Solution{

    public static void main(String[] args){
        ListNode head = new ListNode();
        head.data = 1;
        ListNode node = new ListNode();
        node.data = 1;
        head.next = node;
        ListNode tmp = head;
        while(tmp != null){
            System.out.println(tmp.data);
            tmp = tmp.next;
        }
        tmp = deleteDuplication2(head);
        System.out.println("delete");

        while(tmp != null){

            System.out.println(tmp.data);
            tmp = tmp.next;
        }
    }
    //使用了缓冲区，开了额外空间
    public static ListNode deleteDuplication(ListNode head){
        if(head == null) return head;
        Set<Integer> set = new HashSet();
        ListNode cur = head;
        set.add(cur.data);
        ListNode pre = cur;
        cur = cur.next;
        while(cur != null){
            if(!set.contains(cur.data)){
                set.add(cur.data);
            }
            else{

                pre.next = cur.next;
            }
            pre = pre.next;
            cur = cur.next;
        }
        return head;

    }

    //不使用额外空间，不开缓冲区
    public static ListNode deleteDuplication2(ListNode head){
        if(head == null) return head;
        ListNode master = head;
        while(master != null){
            ListNode pre = master;
            ListNode cur = master.next;
            int value = master.data;
            while(cur != null){
                if(cur.data == value){
                    pre.next = cur.next;
                    cur = pre.next;

                }else{

                    cur.next = cur;
                    pre.next = pre;
                }
            }
            master = master.next;
        }
        return head;
    }
}