C++ 双向循环链表

c++中双向循环链表的第一部分是数据域，用于存储具体的数据信息，这个数据可以是任何类型，取决于具体的应用场景。第二部分是指向前驱节点的指针prev，第三部分是指向后继节点的指针next，同样和prev一样是一个引用或指针。

双向循环链表：头插法，先创建一个节点，将节点的prev指向虚拟头结点，将节点的next指向虚拟头结点的下一个节点，最后将对应节点的指针指向对应位置。

尾插法，先创建一个节点，将节点的prev指向虚拟头结点的prev所指向的指针，将节点的next指针指向虚拟头结点，最后将对应节点的指针指向对应位置。

任意插，找到需要插入的指针后，新节点的prev指向插入节点位置的节点，新节点next指向插入节点位置的下一个节点，最后将节点的指针分别指向对应位置。

节点删除，将节点的前一个节点的next指针指向后一个节点，将后一个节点的prev指向节点前一个节点。并且释放节点的内存。注意，删除的节点不能是虚拟头结点。

代码见下：

#include<iostream>
using namespace std;//双向循环链表
template<typename T>
struct Node {T data;Node* prev;Node* next;Node(const T& value) :data(value), prev(NULL), next(NULL) {}
};template<class T>
class DoublyLinkedList {
public:DoublyLinkedList();~DoublyLinkedList();void push_front(const T& value);void push_back(const T& value);void insert_after(Node<T>* node, const T& value);void delete_node(Node<T>* node);void modify(Node<T>* node, const T& value);Node<T>* find(const T& value) const;void print() const;int size() const;bool empty() const;private:Node<T>* m_dummyHead;int m_size;
};template<class T>
DoublyLinkedList<T>::DoublyLinkedList(): m_size(0)
{m_dummyHead = new Node<T>(T());m_dummyHead->prev = m_dummyHead;m_dummyHead->next = m_dummyHead;
}template<class T>
DoublyLinkedList<T>::~DoublyLinkedList()
{while (m_size > 0) {delete_node(m_dummyHead->next);}delete m_dummyHead;m_dummyHead = NULL;
}template<class T>
void DoublyLinkedList<T>::push_front(const T& value)
{Node<T>* newNode = new Node<T>(value);newNode->prev = m_dummyHead;newNode->next = m_dummyHead->next;m_dummyHead->next->prev = newNode;m_dummyHead->next = newNode;++m_size;
}template<class T>
void DoublyLinkedList<T>::push_back(const T& value)
{Node<T>* newNode = new Node<T>(value);newNode->prev = m_dummyHead->prev;newNode->next = m_dummyHead;m_dummyHead->prev->next = newNode;m_dummyHead->prev = newNode;++m_size;
}template<class T>
void DoublyLinkedList<T>::insert_after(Node<T>* node, const T& value)
{if (node == NULL || node == m_dummyHead) {return;}Node<T>* newNode = new Node<T>(value);newNode->prev = node;newNode->next = node->next;node->next->prev = newNode;node->next = newNode;++m_size;
}template<class T>
void DoublyLinkedList<T>::delete_node(Node<T>* node)
{if (node == NULL || node == m_dummyHead) {return;}node->prev->next = node->next;node->next->prev = node->prev;delete node;--m_size;
}template<class T>
void DoublyLinkedList<T>::modify(Node<T>* node, const T& value)
{if (node == NULL || node == m_dummyHead) {return;}node->data = value;
}template<class T>
Node<T>* DoublyLinkedList<T>::find(const T& value) const
{Node<T>* curr = m_dummyHead->next;while (curr != m_dummyHead) {if (curr->data == value) {return curr;}curr = curr->next;}return NULL;
}template<class T>
void DoublyLinkedList<T>::print() const
{Node<T>* curr = m_dummyHead->next;while (curr != m_dummyHead) {cout << curr->data << " ";curr = curr->next;}cout << endl;
}template<class T>
int DoublyLinkedList<T>::size() const
{return m_size;
}template<class T>
bool DoublyLinkedList<T>::empty() const
{return m_size == 0;
}int main() {DoublyLinkedList<char> dll;dll.push_back('i'); dll.print();dll.push_back('c'); dll.print();dll.push_back('p'); dll.print();dll.push_back('c'); dll.print();dll.push_front('m'); dll.print();dll.push_front('a'); dll.print();Node<char>* nd = dll.find('a');dll.insert_after(nd, 'c'); dll.print();nd = dll.find('m');dll.insert_after(nd, '/'); dll.print();nd = dll.find('i');dll.modify(nd, 'c'); dll.print();nd = dll.find('m');dll.delete_node(nd); dll.print();cout << dll.empty() << endl;cout << dll.size() << endl;return 0;
}

代码练习1 对应蓝桥云课 小王子双链表 代码见下

#include<iostream>
using namespace std;//双向循环链表
template<typename T>
struct Node {T data;Node* prev;Node* next;Node(const T& value) :data(value), prev(NULL), next(NULL) {}
};template<class T>
class DoublyLinkedList {
public:DoublyLinkedList();~DoublyLinkedList();void push_front(const T& value);void push_back(const T& value);void insert_after(Node<T>* node, const T& value);void delete_node(Node<T>* node);void modify(Node<T>* node, const T& value);Node<T>* find(const T& value) const;void print() const;int size() const;bool empty() const;private:Node<T>* m_dummyHead;int m_size;
};template<class T>
DoublyLinkedList<T>::DoublyLinkedList(): m_size(0)
{m_dummyHead = new Node<T>(T());m_dummyHead->prev = m_dummyHead;m_dummyHead->next = m_dummyHead;
}template<class T>
DoublyLinkedList<T>::~DoublyLinkedList()
{while (m_size > 0) {delete_node(m_dummyHead->next);}delete m_dummyHead;m_dummyHead = NULL;
}template<class T>
void DoublyLinkedList<T>::push_front(const T& value)
{Node<T>* newNode = new Node<T>(value);newNode->prev = m_dummyHead;newNode->next = m_dummyHead->next;m_dummyHead->next->prev = newNode;m_dummyHead->next = newNode;++m_size;
}template<class T>
void DoublyLinkedList<T>::push_back(const T& value)
{Node<T>* newNode = new Node<T>(value);newNode->prev = m_dummyHead->prev;newNode->next = m_dummyHead;m_dummyHead->prev->next = newNode;m_dummyHead->prev = newNode;++m_size;
}template<class T>
void DoublyLinkedList<T>::insert_after(Node<T>* node, const T& value)
{if (node == NULL || node == m_dummyHead) {return;}Node<T>* newNode = new Node<T>(value);newNode->prev = node;newNode->next = node->next;node->next->prev = newNode;node->next = newNode;++m_size;
}template<class T>
void DoublyLinkedList<T>::delete_node(Node<T>* node)
{if (node == NULL || node == m_dummyHead) {return;}node->prev->next = node->next;node->next->prev = node->prev;delete node;--m_size;
}template<class T>
void DoublyLinkedList<T>::modify(Node<T>* node, const T& value)
{if (node == NULL || node == m_dummyHead) {return;}node->data = value;
}template<class T>
Node<T>* DoublyLinkedList<T>::find(const T& value) const
{Node<T>* curr = m_dummyHead->next;while (curr != m_dummyHead) {if (curr->data == value) {return curr;}curr = curr->next;}return NULL;
}template<class T>
void DoublyLinkedList<T>::print() const
{Node<T>* curr = m_dummyHead->next;while (curr != m_dummyHead) {cout << curr->data << " ";curr = curr->next;}cout << endl;
}template<class T>
int DoublyLinkedList<T>::size() const
{return m_size;
}template<class T>
bool DoublyLinkedList<T>::empty() const
{return m_size == 0;
}int main() {DoublyLinkedList<int> dll;for (int i = 1; i <= 10; ++i) {dll.push_back(i);}int n;cin >> n;while (n--) {int x;cin >> x;Node<int>* nd = dll.find(x);dll.delete_node(nd);dll.push_front(x);dll.print();}return 0;
}