删除节点

 ListNode* deleteNode(ListNode* head, int val) {
        if(head->val == val){
            head=head->next;
            return head;
        }
        ListNode* front=head->next;
        ListNode* tail=head;
        while(front != NULL){
            if(front->val == val){
                if(front-> next != NULL){
                    tail->next=front->next;
                    break;
                }else{
                    //删除最后一个
                    tail->next=NULL;
                    break;
                }
            }
            front=front->next;
            tail=tail->next;
        }
        return head;
    }