双链表的各种操作 创建 插入 删除 查找

首先定义一下双链表的结点结构

#include<iostream>  using namespace std;  class Node  {      public:          Node()=default;   // c++ 11标准，如果不支持其实就是各种成员值默认都赋0          Node(int val):value(val),pre(nullptr),next(nullptr){}          inline Node*& getPre(){ return pre; }  //  得到前一个结点          inline Node*& getNext(){ return next; }  //得到后一个结点          inline int getValue(){ return value; }   //得到当前结点的值      private:          Node *pre;          Node *next;          int value;  };  void CreateList(Node *&head);   //创建一个双链表  void printLList(Node *head);   //打印双链表  void Insert(Node *&head, size_t pos, int val);  //插入一个结点  void DeleteByValue(Node *&head,int val);     //按给的值删一个元素  void DeleteByPos(Node *&head,size_t position);      //按位置删一个元素  Node* SearchByValue(Node *head, int val, size_t *where=0);    //按值查找  Node* SearchByPos(Node *head, size_t pos, int *val=0);        //按给的位置查找元素  size_t Length(Node *head);   //返回链表的长度  void CreateList(Node *&head)  {      int input;      size_t pos=1;      cout<<"正在创建链表，输入结点值 (ctrl+z 结束输入)"<<endl;    while(cin >> input)          Insert(head,pos++,input);      cout<<"The list was created!"<<endl<<endl;      cin.clear();      return;  }    void Insert(Node *&head, size_t pos, int val)  {      size_t length = Length(head);      if(pos < 1 || pos > (length+1))    // 插入位置不合法       {          cout<<"The given position is illegal!"<<endl<<endl;          return;      }         Node *newNode = new Node(val);      if(pos == 1)   //  表头插入         {          if(head == nullptr)   //空表               head = newNode;          else          //非空表           {              head->getPre() = newNode;              newNode->getNext() = head;              head = newNode;          }      }      else      {          Node *position = SearchByPos(head,pos-1);;           if( pos == (length+1))  //  表尾插入           {              position->getNext() = newNode;              newNode->getPre() = position;          }           else                  //  其他位置插入          {              newNode->getNext() = position->getNext();              newNode->getPre() = position;              position->getNext()->getPre() = newNode;              position->getNext() = newNode;          }      }      return;  }    size_t Length(Node *head)  {      size_t len = 0;      Node *pos = head;      while( pos != nullptr )      {          ++len;          pos = pos->getNext();      }      return len;  }    void DeleteByValue(Node *&head,int val)  {      Node* pos = SearchByValue(head,val);      if(pos == nullptr)      {          cout<<val<<" is not found, cannot delete it!"<<endl<<endl;          return;      }      else if(pos == head)  //  删表头           head = head->getNext();      else if(pos->getNext() != nullptr)  //删其他位置       {          pos->getPre()->getNext() = pos->getNext();          pos->getNext()->getPre() = pos->getPre();      }      else               //删表尾           pos->getPre()->getNext() = nullptr;      delete pos;      pos = nullptr;      cout<<val<<" is deleted!"<<endl<<endl;      return;  }    void DeleteByPos(Node *&head,size_t position)  {      size_t length = Length(head);      if(position < 1 || position > length)      {          cout<<"The position is illegal, cannot delete it!"<<endl<<endl;          return;      }      Node* pos = SearchByPos(head,position);      if(position == 1)  //  删除 表头          head = head->getNext();      else      {          if(pos->getNext() == nullptr)  //删除 表尾               pos->getPre()->getNext() = nullptr;          else                      //删其他位置           {              pos->getPre()->getNext() = pos->getNext();              pos->getNext()->getPre() = pos->getPre();          }      }      delete pos;      pos = nullptr;      cout<<"The value at position "<<position<<" is deleted!"<<endl<<endl;      return;  }    Node* SearchByValue(Node *head, int val, size_t *where)  {      if(where != 0)          ++(*where);      Node *pos = head;      while(pos != nullptr && val != pos->getValue())      {          pos = pos->getNext();          if(where != 0)              ++(*where);      }      if(pos == nullptr)          return nullptr;      else          return pos;  }    Node* SearchByPos(Node *head, size_t pos, int *val)  {      size_t length = Length(head);      if(pos < 1 || pos > length)          return nullptr;      Node *position = head;       size_t temp = 0;      while(position != nullptr && temp < pos-1)      {          ++temp;          position = position->getNext();      }      if(position == nullptr)          return nullptr;      else      {          if(val != 0)              *val = position->getValue();          return position;      }  }      void printLList(Node *head)  {      if(head == nullptr)          cout<<"The list is empty!"<<endl<<endl;      else      {          do          {              cout<<head->getValue()<<" ";              head = head->getNext();          }while(head != nullptr);          cout<<endl<<endl;      }      return;  }  int main(int argc, char** argv)   {      Node *temp;      size_t pos;      int val;      Node *head = nullptr;            CreateList(head);  //创建链表       printLList(head);            cout<<"插入，  输入要插入的位置和要插入的值（位置从1开始）"<<endl;      cin>>pos>>val;      Insert(head,pos,val);      printLList(head);            pos=0;      cout<<"按值查找，  输入要查找的值"<<endl;      cin>>val;      temp = SearchByValue(head,val,&pos);      if(temp == nullptr)          cout<<"The value of "<<val<<" was no found!"<<endl<<endl;      else          cout<<"The value of "<<val<<"  was found! Its position is "<<pos<<endl<<endl;            val=0;      cout<<"按地址查找， 输入要查找的位置"<<endl;      cin>>pos;      temp = SearchByPos(head,pos,&val);      if(temp == nullptr)          cout<<"The value at position "<<pos<<" was no found!"<<endl<<endl;      else          cout<<"The value at position "<<pos<<"  was found! Its value is "<<val<<endl<<endl;            cout<<"按值删除，输入要删除的值"<<endl;      cin>>val;      DeleteByValue(head,val);        printLList(head);                cout<<"按地址删除，输入要删除的位置"<<endl;       cin>>pos;       DeleteByPos(head,pos);       printLList(head);            return 0;  }   

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