一、链表和结点结构体的声明 (ListNode.h)

typedef int data_t;

typedef struct ListNode {		// 结点声明
	data_t data;
	ListNode* next;
	ListNode* prev;
}ListNode;

typedef struct SeqLinkList {
	
	SeqLinkList();
	void list_print();					// 从前往后打印链表
	void list_reverse_print();			// 从后往前打印链表
	size_t size();						// 链表大小（链表结点个数）

	int push_back(data_t val);			// 尾插
	void pop_back();					// 尾删
	int push_front(data_t val);			// 头插
	
	int list_find(data_t val);			// 查找某个结点
	int list_insert(int pos, data_t val);	// 在某个位置插入一个结点
	int list_delete(int pos);				// 删除某个位置的结点
	void list_destroy();					// 释放整个链表

private:
	ListNode* _phead;					// 链表头结点的地址
	ListNode* _ptail;					// 链表尾结点的地址
	size_t _num;						// 链表元素的个数
		
}SeqLinkList;

二、链表各个功能的实现

1、增

(1) 构造函数（创建链表头结点）

创建一个空的头结点，同时初始化元素个数

SeqLinkList::SeqLinkList() {
	_phead = (ListNode*)malloc(sizeof(ListNode));
	assert(_phead);

	_ptail = _phead;		// 此时头尾指向同一个地方

	_num = 0;		// 初始化结点的个数
}

(2) 尾插

int SeqLinkList::push_back(data_t val) {

	ListNode* newNode = (ListNode*)malloc(sizeof(ListNode));
	if (newNode == NULL)
		return -1;

	newNode->data = val;
	newNode->next = NULL;
	newNode->prev = _ptail;
	_ptail->next = newNode;	// 链接新的结点

	_ptail = newNode;		// 尾节点移动
	_num++;

	return 0;
}

(3) 头插

int SeqLinkList::push_front(data_t val) {
	ListNode* newNode = (ListNode*)malloc(sizeof(ListNode));
	if (newNode == NULL)
		return -1;

	ListNode* nextNode = _phead->next;		// _phead的下一个结点
	newNode->data = val;
	newNode->next = nextNode;
	newNode->prev = _phead;
	_phead->next = newNode;
	if (nextNode != NULL)
		nextNode->prev = newNode;

	_num++;

	return 0;
}

(4) 任意位置的插入

int SeqLinkList::list_insert(int pos, data_t val) {
	if (pos > _num - 1)
		return -1;

	ListNode* current = _phead;
	while (pos-- && (current = current->next) != NULL);

	ListNode* nextNode = current->next;			// 记录下当前节点的下一个结点
	ListNode* newNode = (ListNode*)malloc(sizeof(ListNode));
	if (newNode == NULL)
		return -1;

	newNode->data = val;            // 链接新的结点
	current->next = newNode;
	newNode->next = nextNode;
	newNode->prev = current;

	if (nextNode != NULL)
		nextNode->prev = newNode;		// 考虑尾插

	_num++;

	return 0;
}

2、删

(1) 尾删

void SeqLinkList::pop_back() {
	ListNode* tailNode = _ptail;		// 记录尾节点
	_ptail = _ptail->prev;			
	_ptail->next = NULL;
	free(tailNode);
	tailNode = NULL;
	_num--;
}

(2) 任意位置的删除

int SeqLinkList::list_delete(int pos) {
	if (pos > _num - 1)
		return -1;

	ListNode* current = _phead;
	while (pos-- && (current = current->next) != NULL);

	if (current == _phead)
		_phead = current->next;		// 考虑头删
	else
	{
		ListNode* prevNode = current->prev;
		ListNode* nextNode = current->next;
		prevNode->next = nextNode;
		if (nextNode != NULL)
			nextNode->prev = prevNode;
	}
	
	free(current);
	current = NULL;

	_num--;

	return 0;
}

(3) 链表释放

void SeqLinkList::list_destroy() {
	_num++;			// 补上一个头结点，下面是连带着头结点一起释放了
	while (_phead != NULL)
	{
		ListNode* lastNode = _phead;
		_phead = _phead->next;
		free(lastNode);
		lastNode = NULL;
		_num--;
	}
}

3、查

(1) 获取元素个数

size_t SeqLinkList::size() {
	return _num;
}

(2) 正向打印

void SeqLinkList::list_print(){

	ListNode* current = _phead;
	while ((current = current->next) != NULL)
	{
		printf("%d->", current->data);
	}
}

(3) 反向打印

void SeqLinkList::list_reverse_print() {

	ListNode* current = _ptail;
	while (current != _phead)
	{
		printf("%d->", current->data);
		current = current->prev;
	}
}