面试题57 删除链表中重复的结点

题目描述

在一个排序的链表中，存在重复的结点，请删除该链表中重复的结点，重复的结点不保留，返回链表头指针。 例如，链表1->2->3->3->4->4->5 处理后为 1->2->5

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
        val(x), next(NULL) {
    }
};
*/
class Solution {
public:
    ListNode* deleteDuplication(ListNode* pHead)
    {
        if (!pHead)
            return NULL;
        if (!pHead->next)
            return pHead;
        
        ListNode* p = new ListNode(-1);
        ListNode* q = pHead;
        p->next = q;
        ListNode* r = q->next;
        
        ListNode* h = p;
        int flag;
        while (r){
            flag = 0;
            while (r != NULL && q->val == r->val){
                q->next = r->next;
                delete r;
                r = q->next;
                flag = 1;
            }
            if (flag == 1){
                if (r == NULL){
                    p->next = NULL;
                    delete q;
                }
                else{
                    p->next = r;
                    delete q;
                    q = r;
                    r = r->next;
                }
            }
            else{
                p = p->next;
                q = q->next;
                r = r->next;
            }
        }
        return h->next;
    }
};