我们需要更新两者ll.head
and node.next
,所以指向node
除非你想对头部进行特殊处理,否则还不够好。相反,让我们使用指向我们要更新的指针的指针。
void delete_node(node** node_ptr_ptr) {
node* to_delete = *node_ptr_ptr;
*node_ptr_ptr = to_delete->next;
free(to_delete);
}
void delete_every_second(ll* l) {
node** node_ptr_ptr = &( l->head );
while (1) {
if (*node_ptr_ptr == NULL) break;
delete_node(node_ptr_ptr);
if (*node_ptr_ptr == NULL) break;
node_ptr_ptr = &( (*node_ptr_ptr)->next );
}
}
假设您从以下内容开始:
+------+ +------+ +------+ +------+
| head ------>| val | +-->| val | +-->| val |
+------+ +------+ | +------+ | +------+
| next ---+ | next ---+ | next --->NULL
+------+ +------+ +------+
After node** node_ptr_ptr = &( l->head );
:
+------+ +------+ +------+ +------+
| head ------>| val1 | +-->| val2 | +-->| val3 |
+------+ +------+ | +------+ | +------+
^ | next ---+ | next ---+ | next --->NULL
| +------+ +------+ +------+
|
+-----+
|
+------+ |
| ptr ----+
+------+
After node* to_delete = *node_ptr_ptr;
:
+------+
| del ----+
+------+ |
|
+------+
|
v
+------+ +------+ +------+ +------+
| head ------>| val1 | +-->| val2 | +-->| val3 |
+------+ +------+ | +------+ | +------+
^ | next ---+ | next ---+ | next --->NULL
| +------+ +------+ +------+
|
+-----+
|
+------+ |
| ptr ----+
+------+
After *node_ptr_ptr = to_delete->next; free(to_delete);
:
+------+ +------+ +------+
| head -------------------->| val2 | +-->| val3 |
+------+ +------+ | +------+
^ | next ---+ | next --->NULL
| +------+ +------+
|
+-----+
|
+------+ |
| ptr ----+
+------+
After node_ptr_ptr = &( (*node_ptr_ptr)->next );
:
+------+ +------+ +------+
| head -------------------->| val2 | +-->| val3 |
+------+ +------+ | +------+
+---------------->| next ---+ | next --->NULL
| +------+ +------+
|
+------+ |
| ptr ----+
+------+