Remove linked list elements (203)

203. Remove Linked List Elements
     Delete all nodes in the linked list that are equal to the given value val.

Example:
Input: 1->2->6->3->4->5->6, val = 6
Output: 1->2->3->4->5 Create a pseudo-head by
linking the original question
Node:

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
    
    
public:
    ListNode* removeElements(ListNode* head, int val) {
    
    
  if (head == nullptr)
              return nullptr;
          ListNode* sentr = new ListNode();//申请一个伪头结点
          sentr->next = head;
          ListNode* prear = sentr;
          ListNode* pfro = head;
          while (pfro) {
    
    
              if (pfro->val == val) {
    
    
                  prear->next = pfro->next;
                  pfro=pfro->next;
              }
              else{
    
    
              prear = prear->next;
              pfro = pfro->next;
              }
          }
          return sentr->next;
    }
};