题解 | #删除有序链表中重复的元素-II#

链表问题的通用思路，弄一个假的头节点，避免分出精力来处理头节点被删了

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 *	ListNode(int x) : val(x), next(nullptr) {}
 * };
 */
#include <iterator>
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    ListNode* deleteDuplicates(ListNode* head) {
        // write code here
        std::array<int,2001> counters;
        std::fill(counters.begin(),counters.end(),0);
        ListNode *cur=head,*previous,*resultPrev=new ListNode(0);
        while(cur){
            counters[cur->val+1000]++;
            cur=cur->next;
        };
        
        cur=head,previous=resultPrev;
        resultPrev->next=head;

        while(cur){
            //cout<<cur->val<<' '<<counters[cur->val+1000]<<endl;
            if(counters[cur->val+1000]>1){
                previous->next=cur->next;
                //cout<<cur->val<<' '<<cur->next->val<<' '<<counters[cur->val+1000]<<endl;
                cur=cur->next;
                continue;
            }
            previous=cur;
            cur=cur->next;
        };

        return resultPrev->next;

    }
};