C++简单实现双链表

    首先，来了解一下什么是双向链表。官方解释是这样的：双向链表也叫双链表，是链表的一种，它的每个数据结点中都有两个指针，分别指向直接后继和直接前驱。所以，从双向链表中的任意一个结点开始，都可以很方便地访问它的前驱结点和后继结点。

来一波图：

   由上图可以看出：其实双向链表是由很多个节点组成的，而每一个节点又分为三个部分，一个数据域，用于存放数据；两个指针，一个用于指向前一个节点，另一个用于指向后一个节点。而当前边和后边没有节点的时候就指向NULL。

    接下来看具体代码实现：

#include <iostream>using namespace std;#include <assert.h>typedef int DataType;struct Node{Node(const DataType& data): _pNext(NULL), _pPre(NULL), _data(data){}Node* _pNext;Node* _pPre;DataType _data;};class List{public:List()//构造函数: _pHead(NULL){}List(DataType* array, size_t size)//构造函数{for (size_t i = 0; i < size; ++i)PushBack(array[i]);}~List()//析构函数{Node* pTail = _pHead;while ((_pHead) && (_pHead->_pNext)){pTail = _pHead;_pHead = _pHead->_pNext;delete pTail;}delete _pHead;} void PushBack(const DataType data);//后插void PopBack();//后删void PushFront(const DataType data);//前插void PopFront();//前删Node* Find(const DataType data);Node* Erase(Node* pos);//删除任意位置节点Node* Insert(Node* pos, const DataType& data);//任意位置插入size_t Size();//求节点个数 private:Node* _pHead;};void List::PushBack(const DataType data)//后插{Node* pTail = _pHead;Node* pNewNode = new Node(data);if (_pHead == NULL)//空链表{_pHead = pNewNode;pNewNode->_pPre = pTail;}else{while (pTail->_pNext){pTail = pTail->_pNext;}pTail->_pNext = pNewNode;pNewNode->_pPre = pTail;}pNewNode->_data = data;pNewNode->_pNext = NULL;}

void List::PopBack()//后删{Node* pTail = _pHead;if (pTail == NULL){return;}else{while (pTail->_pNext){pTail = pTail->_pNext;}pTail->_pPre->_pNext = NULL;//将删除节点前一节点的pNext指针指向NULLdelete pTail;}}

前插和后插都差不多，这里就以前插为例做一个详细讲解（前删和后删都特别简单，就不多做讲解了）

具体代码：

void List::PushFront(const DataType data)//前插{Node* NewNode = new Node(data);if (_pHead != NULL){_pHead->_pPre = NewNode;}NewNode->_data = data;NewNode->_pNext = _pHead;NewNode->_pPre = NULL;_pHead = NewNode;}

void List::PopFront()//前删{if (_pHead == NULL){return;}else{Node* del = _pHead;_pHead = _pHead->_pNext;_pHead->_pPre = NULL;delete del;}}Node* List::Find(const DataType data)//查找函数{Node* pTail = _pHead;//空链表if (pTail == NULL){return NULL;}//只有一个节点的情况else if ((_pHead->_pNext == NULL) && (_pHead->_data == data)){return _pHead;}//多节点情况else{while (pTail->_pNext){if (data == pTail->_data){return pTail;}pTail = pTail->_pNext;}}return NULL;}

删除任意位置的详解：

具体代码：

Node* List::Erase(Node* pos)//删除任意位置节点{if (NULL == pos){return _pHead;}if (pos == _pHead)//删除头节点{PopFront();}else{pos->_pPre->_pNext = pos->_pNext;pos->_pNext->_pPre = pos->_pPre;delete pos;}return _pHead;}

任意位置插入节点详解：

具体代码：

Node* List::Insert(Node* pos, const DataType& data)//任意位置插入{assert(NULL != pos);Node* NewNode = new Node(data);if (pos == _pHead){PushFront(data);return _pHead;}else if (NULL == pos->_pNext){PushBack(data);return _pHead;}else{NewNode->_pNext = pos;pos->_pPre->_pNext = NewNode;NewNode->_pPre = pos->_pPre;pos->_pPre = NewNode;NewNode->_data = data;return _pHead;}}

size_t List::Size()//求节点个数{if (_pHead == NULL){return 0;}else{size_t count = 1;Node* pTail = _pHead;while (pTail->_pNext){++count;pTail = pTail->_pNext;}return count;}}DataType array[] = { 1, 2, 3, 4, 5, 6 };List list(array, sizeof(array) / sizeof(array[0]));void FunTest1(){list.PushBack(7);list.PopBack();list.PushFront(7);list.PopFront();}void FunTest2(){Node* pos = list.Find(2);list.Erase(pos);Node* position = list.Find(4);list.Insert(position, 8);}void FunTest3(){size_t size = list.Size();cout << "size=" << size << endl;}int main(){FunTest1();FunTest2();FunTest3();return 0;}