牛客OJ：删除链表中重复的节点

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两指针循环（感觉还是三指针好写一些）：

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
        val(x), next(NULL) {
    }
};
*/
class Solution {
public:
    ListNode* deleteDuplication(ListNode* pHead)
    {
        if(pHead == NULL) return NULL;
        ListNode* root = NULL;
        ListNode* fa = pHead;
        ListNode* cld = fa->next;
        ListNode* last = NULL;
        while(cld!=NULL){
            bool flag = false;
            while(cld!=NULL && fa->val == cld->val){
                flag = true;
                delete fa;
                fa = cld;
                cld = cld->next;
            }
            if(flag){
                delete fa;
                if(last != NULL) last->next = cld;
                fa = cld;
                if(cld!=NULL) cld = cld->next;
                continue;
            }
            if(root == NULL) root = fa;
            if(cld == NULL) break;
            last = fa;
            fa = cld;
            cld = cld->next;
        }
        if(root==NULL&&fa!=NULL) root = fa;
        return root;
    }
};