Write a function to delete a node (except the tail) in a singly linked list, given only access to that node.
Supposed the linked list is 1 -> 2 -> 3 -> 4 and you are given the third node with value
3, the linked list should become 1 -> 2 -> 4 after calling your function.
从链表中。删除指定的节点，但又没有给出前指针。所以先交换当前节点和下一节点的值。然后删除下一节点就可以。代码例如以下：
void deleteNode(ListNode* node) {
if (!node || !node->next)
return;
node->val = node->next->val;
node->next = node->next->next;
}