重复节点删除

方法一：哈希表记录遍历一次，再遍历一次删除重复元素

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
        val(x), next(NULL) {
    }
};
*/
class Solution {
public:
    ListNode* deleteDuplication(ListNode* pHead) {
        unordered_map<int,int> m;
        ListNode* head = new ListNode(-1);
        head->next = pHead;
        while(pHead){
           ++m[pHead->val];
            pHead = pHead->next;
        }
        pHead = head;
        while(pHead->next){
            if(m[pHead->next->val]>1){
                ListNode* tmp = pHead->next;
                pHead->next = pHead->next->next;
                delete tmp;
            }else{
            pHead = pHead->next;
            }
        }
        return head->next;
    }
};