83. Remove Duplicates from Sorted List

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public:    ListNode* deleteDuplicates(ListNode* head) {        ListNode* p = head;        if(head == NULL){            return head;        }        ListNode* q = head->next;        if( p != NULL){            while(q !=NULL){                if(q->val == p->val){                    p->next = q->next;                }                else{                    //p->next = q;                    //这个时候p的next是指向q的list不会断                    p = q;                    //q = p->next;                }                //q每次都是需要向后移动的                q = q->next;            }            return head;                   }        else{            return head;        }            }};