题解 | 删除链表中重复的结点

//三指针法，每次删除头部，利用flag做标记； 利用循环也可！
/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
        val(x), next(NULL) {
    }
};
*/
class Solution {
public:
    ListNode* deleteDuplication(ListNode* pHead) {
        ListNode* dummynode = new ListNode(-1);
        dummynode->next = pHead;
        if (pHead == nullptr) return nullptr;
        ListNode* pre = dummynode;
        ListNode* cur = pHead;
        ListNode* nex = cur->next;
        bool flag = false;
        while (nex) {
            ListNode* last = nex->next;
            if (cur->val == nex->val) {
                pre->next = nex;
                cur = nex;
                nex = last;
                flag = true;
            }
            else {
                if (flag) {
                    pre->next = nex;
                    cur = nex;
                    nex = last;
                    flag = !flag;
                }
                else {
                    pre = cur;
                    cur = nex;
                    nex = last;
                }
            }
        }
        if (flag) {
            pre->next = nex;
        }
        return dummynode->next;
    }
};