CD47.【C++ Dev】list的模拟实现(2)
目录
1.const修饰的迭代器的实现
方法1:分成两个类
完整代码
方法2:STL库的写法
2.STL库的第三个模版参数T*的解释
->->的简写语法
3.其他成员函数
insert
erase
push_back、push_front、pop_front、pop_back
size
clear
析构函数~list()
拷贝构造函数(★)
私有函数empty_initialize
swap
operator=
4.提交到leetcode题上测试成员函数的正确性
代码
提交结果
承接CD46.【C++ Dev】list的模拟实现(1)文章
1.const修饰的迭代器的实现
回顾const修饰的迭代器的要求:1.自己可以修改 2.指向的数据不能修改
方法1:分成两个类
const修饰的迭代器和非const修饰的迭代器分成两个类,写两份代码,这两份代码仅仅是operator*的返回的参数不同
//const修饰的迭代器
const T& operator*()
{return node->data;
}//非const修饰的迭代器
T& operator*()
{return node->data;
}注意:const修饰的迭代器中的operator*不能写成T& operator*() const,这个const修饰的是this指针指向的对象node不能被修改(在CD22.【C++ Dev】类和对象(13) 流提取运算符的重载和const成员文章讲过),不是指node->data不能修改
完整代码
#pragma once
namespace mystl
{template<class T>struct __list_node{typedef __list_node<T>* link_type;__list_node(const T& x = T()):next(nullptr), prev(nullptr), data(x){}link_type next;link_type prev;T data;};template<class T>struct __list_iterator{typedef __list_node<T>* link_type;typedef __list_iterator<T> iterator;__list_iterator(link_type x):node(x){}iterator& operator++(){node = node->next;return *this;}iterator operator++(int){iterator tmp(*this);node = node->next;return tmp;}iterator& operator--(){node = node->prev;return *this;}iterator operator--(int){iterator tmp(*this);node = node->prev;return tmp;}bool operator!=(const iterator& x) const{return node != x.node;}bool operator==(const iterator& x) const{return node == x.node;}T& operator*(){return node->data;}link_type node;};template<class T>struct __list_const_iterator{typedef __list_node<T>* link_type;typedef __list_const_iterator<T> const_iterator;__list_const_iterator(link_type x):node(x){}const_iterator& operator++(){node = node->next;return *this;}const_iterator operator++(int){const_iterator tmp(*this);node = node->next;return tmp;}const_iterator& operator--(){node = node->prev;return *this;}const_iterator operator--(int){const_iterator tmp(*this);node = node->prev;return tmp;}bool operator!=(const const_iterator& x) const{return node != x.node;}bool operator==(const const_iterator& x) const{return node == x.node;}const T& operator*(){return node->data;}link_type node;};template<class T>class list{typedef __list_node<T> list_node;typedef __list_node<T>* link_type;public:typedef __list_iterator<T> iterator;typedef __list_const_iterator<T> const_iterator;list(){node = new list_node;node->next = node;node->prev = node;}void push_back(const T& x){link_type tmp = new list_node(x);//先找尾link_type tail = node->prev;tail->next = tmp;tmp->prev = tail;tmp->next = node;node->prev = tmp;}iterator begin(){//返回哨兵位的下一个节点return node->next;}iterator end(){//返回哨兵位return node;}const_iterator begin() const{//返回哨兵位的下一个节点return node->next;}const_iterator end() const{//返回哨兵位return node;}private:link_type node;};
}测试代码:
#include <iostream>
#include "list.h"
void print_list(const mystl::list<int>& ls)//权限缩小
{mystl::list<int>::const_iterator it = ls.begin();while (it != ls.end()){std::cout << *it << " ";it++;}}
int main()
{mystl::list<int> ls;ls.push_back(1);ls.push_back(2);ls.push_back(3);print_list(ls);return 0;
}运行结果:
方法2:STL库的写法
STL的源码:__list_iterator迭代器类有3个模版参数:T、Ref、Ptr
template<class T, class Ref, class Ptr>
struct __list_iterator {typedef __list_iterator<T, T&, T*> iterator;typedef __list_iterator<T, const T&, const T*> const_iterator;typedef __list_iterator<T, Ref, Ptr> self;//......typedef Ref reference;//......reference operator*() const { return (*node).data; }
}
operator*的返回类型为reference,而reference为Ref,Ref是__list_iterator类的第二个模版参数
这样可以为Ref指定:T&或者const T&,这样可以简写const修饰和非const修饰的迭代器,没有必要写两份代码
之前返回类型为iterator要改成__list_iterator<T, Ref>,可以重定义为self
其实是让编译器来代替我们写iterator和const_iterator这两个类
template<class T,class Ref>
struct __list_iterator
{typedef __list_node<T>* link_type;typedef __list_iterator<T,T&> iterator;typedef __list_iterator<T,const T&> const_iterator;typedef __list_iterator<T, Ref> self;typedef Ref reference;__list_iterator(link_type x):node(x){}self& operator++(){node = node->next;return *this;}self operator++(int){self tmp(*this);node = node->next;return tmp;}self& operator--(){node = node->prev;return *this;}self operator--(int){self tmp(*this);node = node->prev;return tmp;}bool operator!=(const self& x) const{return node != x.node;}bool operator==(const self& x) const{return node == x.node;}reference operator*(){return node->data;}link_type node;
};继续测试之前的代码,运行结果:
2.STL库的第三个模版参数T*的解释
上方代码实现的__list_iterator只有2个模版参数,但是STL库却有3个模板参数:
template<class T, class Ref, class Ptr>
struct __list_iterator
{//......
}看看Ptr出现在什么函数中:
STL库将Ptr重定义为pointer:
typedef Ptr pointer;那就找pointer还出现在哪里:
#ifndef __SGI_STL_NO_ARROW_OPERATORpointer operator->() const { return &(operator*()); }
#endif /* __SGI_STL_NO_ARROW_OPERATOR */发现:pointer是operator->的返回类型,原因:
迭代器的任务是模拟指针,而结构体指针是可以用operator->来访问其指向对象的成员,那迭代器也要有operator->操作符
那自制的operator->可以这样写:
template<class T,class Ref,class Ptr>
struct __list_iterator
{typedef __list_node<T>* link_type;typedef __list_iterator<T,T&,T*> iterator;typedef __list_iterator<T,const T&,const T*> const_iterator;typedef __list_iterator<T, Ref,Ptr> self;typedef Ref reference;typedef Ptr pointer;//......reference operator*(){return node->data;}pointer operator->(){return &(node->data);}link_type node;
};
当然也可以复用operator*,写成:
pointer operator->()
{return &(operator*());
}测试代码:
#include <iostream>
#include "list.h"
class Myclass
{
public:Myclass(const int val1=0, const char val2='\0'):_val1(val1), _val2(val2){}int _val1;char _val2;
};int main()
{mystl::list<Myclass> ls;ls.push_back(Myclass(1,'a'));ls.push_back(Myclass(2, 'b'));ls.push_back(Myclass(3, 'c'));mystl::list<Myclass>::iterator it = ls.begin();while (it != ls.end()){std::cout << it->_val1 << " " << it->_val2 << std::endl;std::cout << (*it)._val1 << " " << (*it)._val2 << std::endl;it++;}return 0;
}运行结果:
发现it->_val1和(*it)._val1的效果是等价的
->->的简写语法
注意到operator->()返回的是Myclass*,严谨来说Myclass*是不能访问_val1和_val2的,应该写成
std::cout << it->->_val1 << " " << it->->_val2 << std::endl;但编译器在编译时自动加上了第二个->,C++标准只允许写一个->,提高运算符重载的可读性
3.其他成员函数
insert
和STL保持一致:
这里只实现第一个:
先生成新节点,再在pos前插入:
iterator insert(iterator pos,const T& val)
{link_type newnode = new list_node(val);newnode->prev = pos.node->prev;newnode->next = pos.node;pos.node->prev->next = newnode;pos.node->prev = newnode;return newnode;
}测试代码:
#include <iostream>
#include "list.h"
int main()
{mystl::list<int> ls;ls.push_back(1);ls.push_back(2);ls.push_back(3);auto new_it1=ls.insert(++ls.begin(), 4);//在2的前面插入4for (auto a : ls)std::cout << a << " ";return 0;
}运行结果:
erase
和STL保持一致:
这里只实现第一个:
注意:erase不能删哨兵位,因此先断言
erase函数在删除元素时,会使当前迭代器失效n并返回指向下一个元素的迭代器,因此不能返回void
iterator erase(iterator pos)
{assert(pos != end());iterator ret = pos.node->next;pos.node->prev->next = pos.node->next;pos.node->next->prev = pos.node->prev;delete pos.node;return ret;
}测试代码:
#include <iostream>
#include "list.h"
int main()
{mystl::list<int> ls;ls.push_back(1);ls.push_back(2);ls.push_back(3);ls.erase(++ls.begin());//删除2for (auto a : ls)std::cout << a << " ";return 0;
}运行结果:
push_back、push_front、pop_front、pop_back
可以复用insert和erase的代码
void push_back(const T& x)
{insert(end(), x);
}void push_front(const T& x)
{insert(begin(), x);
}
void pop_front()
{erase(begin());
}
void pop_back()
{erase(--end());
}测试代码:
#include <iostream>
#include "list.h"
int main()
{mystl::list<int> ls;ls.push_back(1);ls.push_back(2);ls.push_back(3);ls.push_back(4);ls.pop_back();ls.pop_front();ls.push_back(5);ls.push_front(6);for (auto a : ls)std::cout << a << " ";return 0;
}运行结果:
size
STL库的实现:
size_type size() const {size_type result = 0;distance(begin(), end(), result);return result;
}distance是算法库<algorithm>中的函数,用于计算两个迭代器之间的距离,并将结果存储到result中,这里我们实现的简单一些:
void distance(const_iterator begin, const_iterator end, size_type& result) const
{const_iterator it = begin;while (it != end){it++;result++;}
}
size_type size() const
{size_type result = 0;distance(begin(), end(), result);return result;
}测试代码:
#include <iostream>
#include "list.h"
int main()
{mystl::list<int> ls;ls.push_back(1);ls.push_back(2);ls.push_back(3);ls.push_back(4);std::cout << ls.size();return 0;
}(当然这样遍历一遍是有缺点的,比较耗时,可以为list类引入第二个成员变量size来存储链表的长度,这里省略不写)
运行结果:
clear
和STL保持一致:
删除多余节点,只保留哨兵位
void clear()
{iterator it = begin();while (it != end())it=erase(it);//应对迭代器失效,接收返回值
}测试代码:
#include <iostream>
#include "list.h"
int main()
{mystl::list<int> ls;ls.push_back(1);ls.push_back(2);ls.push_back(3);for (auto a : ls)std::cout << a << " ";ls.clear();ls.push_back(4);ls.push_back(5);ls.push_back(6);for (auto b : ls)std::cout << b << " ";return 0;
}运行结果:
析构函数~list()
先调用clear(),再将node释放,最后置为空指针
~list()
{clear();delete node;node = nullptr;
}拷贝构造函数(★)
注意是深拷贝,浅拷贝会出问题(在CD44.【C++ Dev】vector模拟实现(3)文章的深拷贝问题解决提到过)
方法:通过遍历的方式一个个拷贝
//const修饰,防止权限放大
list(const list<T>& ls)//必须是引用,这个&如果不写,会无限调用拷贝构造函数
{//准备哨兵位node = new list_node;node->next = node;node->prev = node;//添加节点for (auto& a : ls)//使用引用,节省时间{push_back(a);}
}测试代码:
#include <iostream>
#include "list.h"
int main()
{mystl::list<int> ls;ls.push_back(1);ls.push_back(2);ls.push_back(3);mystl::list<int> ls_copy(ls);for (auto a : ls_copy)std::cout << a<<" ";return 0;
}运行结果:
私有函数empty_initialize
两种构造函数的部分代码有些冗余
可以封装成一个私有函数empty_initialize(),当然库里面也是这样实现的:
swap
和STL保持一致:
注:上面swap的参数:list& x的list是类名,不是类型,却也可以做参数,C++的语法支持这样做,但不建议这样写,代码不直观
交换链表其实是交换头节点
void swap(list<T>& ls)//写成void swap(list& ls)也可以
{std::swap(node, ls.node);
}测试代码:
#include <iostream>
#include "list.h"
int main()
{mystl::list<int> ls1; ls1.push_back(1); ls1.push_back(2); ls1.push_back(3);mystl::list<int> ls2; ls2.push_back(4); ls2.push_back(5); ls2.push_back(6);std::cout << "ls1:";for (auto a : ls1) std::cout << a << " ";std::cout << std::endl << "ls2:";for (auto b : ls2) std::cout << b << " ";ls1.swap(ls2);std::cout << std::endl << "ls1:";for (auto a : ls1) std::cout << a<<" ";std::cout << std::endl << "ls2:";for (auto b : ls2) std::cout << b<<" ";return 0;
}运行结果:
operator=
使用CD40.【C++ Dev】string类的模拟实现(4)(operator=、拷贝构造函数的现代写法、写时拷贝的简单了解)文章提到的现代写法:1.operator=的参数需要调用拷贝构造 2.调用swap
list<T>& operator=(list<T> tmp)//写成list& operator=(list tmp)也可以
{swap(tmp);return *this;
}测试代码:
#include <iostream>
#include "list.h"
int main()
{mystl::list<int> ls1; ls1.push_back(1); ls1.push_back(2); ls1.push_back(3);mystl::list<int> ls2 = ls1;std::cout << "ls2:";for (auto a : ls2) std::cout << a << " ";return 0;
}4.提交到leetcode题上测试成员函数的正确性
题:https://leetcode.cn/problems/design-linked-list/
你可以选择使用单链表或者双链表，设计并实现自己的链表。
单链表中的节点应该具备两个属性：
val和next。val是当前节点的值，next是指向下一个节点的指针/引用。如果是双向链表，则还需要属性
prev以指示链表中的上一个节点。假设链表中的所有节点下标从 0 开始。实现
MyLinkedList类：
MyLinkedList()初始化MyLinkedList对象。int get(int index)获取链表中下标为index的节点的值。如果下标无效，则返回-1。void addAtHead(int val)将一个值为val的节点插入到链表中第一个元素之前。在插入完成后，新节点会成为链表的第一个节点。void addAtTail(int val)将一个值为val的节点追加到链表中作为链表的最后一个元素。void addAtIndex(int index, int val)将一个值为val的节点插入到链表中下标为index的节点之前。如果index等于链表的长度，那么该节点会被追加到链表的末尾。如果index比长度更大，该节点将 不会插入 到链表中。void deleteAtIndex(int index)如果下标有效，则删除链表中下标为index的节点。示例：
输入 ["MyLinkedList", "addAtHead", "addAtTail", "addAtIndex", "get", "deleteAtIndex", "get"] [[], [1], [3], [1, 2], [1], [1], [1]] 输出 [null, null, null, null, 2, null, 3]解释 MyLinkedList myLinkedList = new MyLinkedList(); myLinkedList.addAtHead(1); myLinkedList.addAtTail(3); myLinkedList.addAtIndex(1, 2); // 链表变为 1->2->3 myLinkedList.get(1); // 返回 2 myLinkedList.deleteAtIndex(1); // 现在，链表变为 1->3 myLinkedList.get(1); // 返回 3提示：
0 <= index, val <= 1000- 请不要使用内置的 LinkedList 库。
- 调用
get、addAtHead、addAtTail、addAtIndex和deleteAtIndex的次数不超过2000。
代码
namespace mystl
{template<class T>struct __list_node{typedef __list_node<T>* link_type;__list_node(const T& x = T()):next(nullptr), prev(nullptr), data(x){}link_type next;link_type prev;T data;};template<class T,class Ref,class Ptr>struct __list_iterator{typedef __list_node<T>* link_type;typedef __list_iterator<T,T&,T*> iterator;typedef __list_iterator<T,const T&,const T*> const_iterator;typedef __list_iterator<T, Ref,Ptr> self;typedef Ref reference;typedef Ptr pointer;__list_iterator(link_type x):node(x){}self& operator++(){node = node->next;return *this;}self operator++(int){self tmp(*this);node = node->next;return tmp;}self& operator--(){node = node->prev;return *this;}self operator--(int){self tmp(*this);node = node->prev;return tmp;}bool operator!=(const self& x) const{return node != x.node;}bool operator==(const self& x) const{return node == x.node;}reference operator*(){return node->data;}pointer operator->(){return &(node->data);}link_type node;};template<class T>class list{typedef __list_node<T> list_node;typedef __list_node<T>* link_type;typedef size_t size_type;public:typedef __list_iterator<T, T&, T*> iterator;typedef __list_iterator<T, const T&, const T*> const_iterator;list(){empty_initialize();}list(const list<T>& ls){empty_initialize();for (auto& a : ls){push_back(a);}}void push_back(const T& x){insert(end(), x);}iterator begin(){return node->next;}iterator end(){//返回哨兵位return node;}const_iterator begin() const{return node->next;}const_iterator end() const{return node;}iterator insert(iterator pos,const T& val){link_type newnode = new list_node(val);newnode->prev = pos.node->prev;newnode->next = pos.node;pos.node->prev->next = newnode;pos.node->prev = newnode;return newnode;}iterator erase(iterator pos){assert(pos != end());iterator ret = pos.node->next;pos.node->prev->next = pos.node->next;pos.node->next->prev = pos.node->prev;delete pos.node;return ret;}void push_front(const T& x){insert(begin(), x);}void pop_front(){erase(begin());}void pop_back(){erase(--end());}void distance(const_iterator begin, const_iterator end, size_type& result) const{const_iterator it = begin;while (it != end){it++;result++;}}size_type size() const {size_type result = 0;distance(begin(), end(), result);return result;}void clear(){iterator it = begin();while (it != end())it=erase(it);}void swap(list<T>& ls){std::swap(node, ls.node);}list<T>& operator=(list<T> tmp){swap(tmp);return *this;}~list(){clear();delete node;node = nullptr;}private:void empty_initialize(){node = new list_node;node->next = node;node->prev = node;}link_type node;};
}class MyLinkedList {
public:MyLinkedList() {}mystl::list<int>::iterator getiterator(int index){mystl::list<int>::iterator it=ls.begin();while(index--)it++;return it;}int get(int index) {if (index<ls.size())return getiterator(index).node->data; return -1; }void addAtHead(int val) {ls.push_front(val);}void addAtTail(int val) {ls.push_back(val);}void addAtIndex(int index, int val) {if (index<=ls.size())//取等是尾插ls.insert(getiterator(index),val);}void deleteAtIndex(int index) {if (index<ls.size())ls.erase(getiterator(index));}mystl::list<int> ls;
};提交结果
