双链表

双向链表

1. 双向链表的定义

双向带头循环链表

typedef struct ListNode
{   
	LTDataType data;
	struct ListNode *prev;
	struct ListNode *next;
}LTNode;

2. 链表初始化

LTNode* ListInit()
{
   LTNode* phead = (LTNode*)malloc(sizeof(LTNode));
   phead->next = phead;
   phead->prev = phead;

   return phead;
};

3. 创建新的节点

LTNode* BuyListNode(LTDataType x)
{
	LTNode* newnode = (LTNode*)malloc(sizeof(LTNode));
	newnode->data = x;
	newnode->next = NULL;
	newnode->prev = NULL;

	return newnode;
};

4. 尾插

void ListPushBack(LTNode* phead,LTDataType x)
{
   assert(phead);
   LTNode* tail = phead->prev;
   LTNode* newnode =(LTNode*)malloc(sizeof(LTNode));
   newnode->data = x;

   tail->next = newnode;
   newnode->prev = tail;
   newnode->next = phead;
   phead->prev = newnode;
};

5. 头插

void ListPushFront(LTNode* phead,LTDataType x)
{
	assert(phead != NULL);
    LTNode* newnode = BuyListNode(x);
	LTNode* tail = phead->next;
	phead->next = newnode;
	newnode->prev = phead;
	newnode->next = tail;
	tail->prev = newnode;
};

6. 尾删

void ListPopBack(LTNode* phead)
{
    assert(phead != NULL);
	assert(phead->next != phead);
	LTNode* tail = phead->prev;
	LTNode* tailprev = tail->prev;
	free(tail);
	tailprev->next = phead;
	phead->prev = tailprev;
};

7. 头删

void ListPopFront(LTNode* phead)
{
	assert(phead != NULL);
	assert(phead->next != phead);
	LTNode* tail = phead->next;
	LTNode* next = tail->next;
	free(tail);
	phead->next = next;
	next->prev = phead;
};

8. pos位置删除

void ListErase(LTNode* pos)
{
	assert(pos != NULL);
	LTNode* posPrev = pos->prev;
	LTNode* posNext = pos->next;
    free(pos);
	posPrev->next = posNext;
	posNext->prev = posPrev;
};

9. 查找

LTNode* ListFind(LTNode* phead,LTDataType x)
{
    assert(phead);
	LTNode* cur = phead->next;
	while(cur != phead)
	{
		if(cur->data == x)
		{
		  return cur; 
		}
	    cur = cur->next; 
	}
	return NULL;
};

10. pos位置之前插入

void ListInsert(LTNode* pos,LTDataType x)
{
	assert(pos != NULL);
	LTNode* posPrev = pos->prev;
	LTNode* newnode = BuyListNode(x);
	posPrev->next = newnode;
	newnode->prev = posPrev;
	newnode->next = pos;
	pos->prev = newnode;
};

11. pos位置删除

void ListErase(LTNode* pos)
{
	assert(pos != NULL);
	LTNode* posPrev = pos->prev;
	LTNode* posNext = pos->next;

	posPrev->next = posNext;
	posNext->prev = posPrev;
	free(pos);
};

12.双向链表的销毁

void ListDestroy(LTNode* phead)
{
	assert(phead != NULL);
	LTNode* cur = phead->next;
	while(cur != phead)
	{
		LTNode* next = cur->next;
	    free(cur);
		cur = next;
	}
	free(phead);      
};

用完Destroy后要将传过来的指针手动置空，这是因为要保证传参结构的一致性（都是传一级指针），如果要在Destroy内置空，要用二级指针实现。