Leetcode: 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

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Using a dummy node in head to simplify the procedure!

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//code

class Solution {

public:

       ListNode* removeElements(ListNode* head, int val) {

              //check input

              //if(head==NULL)return head;

              ListNode *p = head, *tmp = head, *dum = new ListNode(-1);

              dum->next = head;

              p = dum;

              while (p->next != NULL){

                     if (p->next->val == val){

                           tmp = p->next;

                           p->next = tmp->next;

                           delete tmp;

                     }

                     else p = p->next;

              }

              head = dum->next;

              delete dum;

              return head;

       }

};