编写代码，移除未排序链表中的重复节点。保留最开始出现的节点。

自己解

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* removeDuplicateNodes(ListNode* head) {
        if(head == NULL)
            return NULL;
        map<int,int> m;
        ListNode* p = head;
        ListNode* pre = head;
        while(head)
        {
            if(m[head->val] == 0)
            {
                m[head->val]++;
                pre = head;
            }                
            else
            {
               pre->next = head->next;
            }
            head = head->next;
        }
        return p;
    }
};

image.png

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* removeDuplicateNodes(ListNode* head) {
        if(head == NULL)
            return NULL;
        ListNode* p = head;
        while(p)
        {
            ListNode* fast = p;
            while(fast->next)
            {
                if(fast->next->val == p->val)
                    fast->next = fast->next->next;
                else
                    fast = fast->next;
            }
            p = p->next;
        }
        return head;
    }
};