[Leetcode]203. Remove Linked List Elements

Remove all elements from a linked list of integers that have value val.

Example
Given: 1 --> 2 --> 6 --> 3 --> 4 --> 5 --> 6, val = 6

Return: 1 --> 2 --> 3 --> 4 --> 5

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public:    ListNode* removeElements(ListNode* head, int val) {        ListNode* ptr = new ListNode(0);        ptr->next = head;        ListNode* pre =ptr;        ListNode* p = head;        while (p != NULL)        {            if (p->val == val)            {                p = p->next;                pre->next = p;            }            else            {                pre = p;                p = p->next;            }        }        pre = ptr->next;        delete ptr;        return pre;    }};