1. Remove Linked List Elements My Submissions QuestionEditorial Solution
   
   Total Accepted: 61924 Total Submissions: 215788 Difficulty: Easy
   
   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

思路：先找到第一个不等于指定值的首节点，作为返回值

另外在过程中过滤掉等于val值的节点并使前面一个不为val值得节点指向下一个不为val值的节点

时间复杂度：O(n)

空间复杂度：O(1)

/**

 * 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) {

        if(head==NULL)return NULL;

        while(head!=NULL&&head->val==val)head=head->next;//找到第一个头部

        ListNode *p=head,*prep=head;

        while(p!=NULL){

            prep=p;

            p=p->next;

            while(p!=NULL&&p->val==val)p=p->next;//直到找到下一个不为val的节点并指向它

            prep->next = p;

        }

        return head;

    }

};