cci-Q2.1 未排序链表去重

原文：

Write code to remove duplicates from an unsorted linked list.

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How would you solve this problem if a temporary buffer is not allowed?

译文：

从一个未排序的链表中移除重复的项

进一步地，

如果不允许使用临时的缓存，你如何解决这个问题？

首先定义一个node类

public class LinkedListNode {    int data;    LinkedListNode next;    public LinkedListNode(int data) {        this.data = data;        this.next = null;    }}

1，允许使用临时的缓存，使用一个哈希表，如果遇到没有遇到过的元素写入哈希表，如果遇到的是重复的，删除。

public static void main(String args[]) {        LinkedListNode head = null;        LinkedListNode tmp = null;        int a[] = {1, 2, 3, 3, 2, 1, 4};        for (int i = 0; i < a.length; i++) {            LinkedListNode next = new LinkedListNode(a[i]);            if (i == 0) {                head = tmp = next;                continue;            }            tmp.next = next;            tmp = next;        }        // Print the list(before)         tmp = head;        while (tmp != null) {            System.out.println(tmp.data);            tmp = tmp.next;        };        delDup1(head);        // Print the list(after)         while (head != null) {            System.out.println(head.data);            head = head.next;        };    }    public static void delDup1(LinkedListNode head) {        LinkedListNode n = head;        Hashtable<Integer, Integer> table = new Hashtable<Integer, Integer>();        LinkedListNode previous = null;        while (n != null) {            if (table.containsKey(new Integer(n.data))) {                previous.next = n.next;            } else {                table.put(new Integer(n.data), new Integer(1));                previous = n;            }            n = n.next;        }    }

2，不允许使用临时的缓存

 public static void main(String args[]) {        LinkedListNode head = null;        LinkedListNode tmp = null;        int a[] = {1, 2, 3, 3, 2, 1, 4};        for (int i = 0; i < a.length; i++) {            LinkedListNode next = new LinkedListNode(a[i]);            if (i == 0) {                head = tmp = next;                continue;            }            tmp.next = next;            tmp = next;        }        // Print the list(before)         tmp = head;        while (tmp != null) {            System.out.println(tmp.data);            tmp = tmp.next;        };        delDup(head);        // Print the list(after)         while (head != null) {            System.out.println(head.data);            head = head.next;        };    }    public static void delDup(LinkedListNode head) {        if (head == null) {            return;        }        LinkedListNode runner = head;        LinkedListNode runnernext = head;        LinkedListNode current = head;        while (current != null) {            runner = current;            runnernext = current.next;            int currentData = current.data;            while (runnernext != null) {                if (runnernext.data == currentData) {                    runner.next = runnernext.next;                    runnernext = runner.next;                } else {                    runner = runnernext;                    runnernext = runner.next;                }            }            current = current.next;        }    }