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

Example:    

Input:  1->2->6->3->4->5->6, val = 6
Output: 1->2->3->4->5

2、解答： 去除链表中指定的值，需要考虑链表中的第一个值为val 和全部为val的情况

3、C++代码

class Solution {
public:
    ListNode* removeElements(ListNode* head, int val) {
        if(head == NULL)
            return NULL;
        
        while(head != NULL && head->val == val)     //若head等与val 则把head指针后移
            head = head->next;
        
        ListNode *curr = head;
        while(curr && curr->next){
            if(curr->next->val == val){
                ListNode *temp = curr->next;
                curr->next = curr->next->next;
                delete temp;
            }else{
                curr = curr->next;
            }   
        }
        
        return head;
    }
};

python代码：

class Solution:
    def removeElements(self, head, val):
        """
        :type head: ListNode
        :type val: int
        :rtype: ListNode
        """
        
        prev = None
        
        curr = head
        
        while curr:
            if curr.val == val:
                if prev:
                    prev.next = curr.next
                else:
                    head = curr.next                   //注意这个地方
            else:
                prev = curr
            
            curr = curr.next
        
        return head