C++基础知识7 list
list
- 1. list的介绍及使用
- 1.1 list的介绍
- 1.2 list的使用
- 1.2.1 list的构造
- 1.2.2 list iterator的使用
- 1.2.3 list capacity
- 1.2.4 list element access
- 1.2.5 list modifiers
- 1.2.6 list的迭代器失效
- 2.1 模拟实现list
1. list的介绍及使用
1.1 list的介绍
1.2 list的使用
1.2.1 list的构造
1.2.2 list iterator的使用
此处，大家可暂时将迭代器理解成一个指针，该指针指向list中的某个节点。
【注意】
- begin与end为正向迭代器，对迭代器执行++操作，迭代器向后移动
- rbegin(end)与rend(begin)为反向迭代器，对迭代器执行++操作，迭代器向前移动
1.2.3 list capacity
1.2.4 list element access
1.2.5 list modifiers
1.2.6 list的迭代器失效
前面说过，此处大家可将迭代器暂时理解成类似于指针，迭代器失效即迭代器所指向的节点的无
效，即该节点被删除了。因为list的底层结构为带头结点的双向循环链表，因此在list中进行插入
时是不会导致list的迭代器失效的，只有在删除时才会失效，并且失效的只是指向被删除节点的迭
代器，其他迭代器不会受到影响。
使用接口
#include<iostream>
#include<algorithm>
#include<list>
#include<vector>
using namespace std;
void test_list1()
{
list<int> lt;
lt.push_back(1);
lt.push_back(2);
lt.push_back(3);
lt.push_back(4);
list<int>::iterator it = lt.begin();
while (it != lt.end())
{
cout << *it << " ";
++it;
}
cout << endl;
for (auto e : lt)
{
cout << e << " ";
}
cout << endl;
}
支持迭代器就支持范围for
struct A
{
public:
A(int a1 = 1, int a2 = 1)
:_a1(a1)
, _a2(a2)
{
cout << "A(int a1 = 1, int a2 = 1)" << endl;
}
A(const A& aa)
:_a1(aa._a1)
, _a2(aa._a2)
{
cout << "A(const A& aa)" << endl;
}
int _a1;
int _a2;
};
void test_list2()
{
list<A> lt;
A aa1(1, 1);
lt.push_back(aa1);
lt.push_back(A(2, 2));//匿名对象
}
传参走隐式类型转换
void test_list3()
{
list<int> lt;
lt.push_back(1);
lt.push_back(2);
lt.push_back(3);
lt.push_back(4);
lt.push_back(5);
lt.push_back(6);
for (auto e : lt)
{
cout << e << " ";
}
cout << endl;
auto it = lt.begin();
int k = 3;
while (k--)
{
++it;
}
lt.insert(it, 30);
for (auto e : lt)
{
cout << e << " ";
}
cout << endl;
int x = 0;
cin >> x;
it = find(lt.begin(), lt.end(), x);
if (it != lt.end())
{
lt.erase(it);
}
for (auto e : lt)
{
cout << e << " ";
}
cout << endl;
}
list迭代器只支持了+±-运算符的重载，因此实现+=智能通过++实现
void test_list4()
{
list<int> lt;
lt.push_back(1);
lt.push_back(20);
lt.push_back(3);
lt.push_back(5);
lt.push_back(4);
lt.push_back(5);
lt.push_back(6);
for (auto e : lt)
{
cout << e << " ";
}
cout << endl;
// 升序
// lt.sort();
// 降序 - 仿函数
// less<int> ls;
// greater<int> gt;
// lt.sort(gt);
lt.sort(greater<int>());
lt.reverse();//类方法
reverse(lt.begin(), lt.end());//算法库实现的
for (auto e : lt)
{
cout << e << " ";
}
cout << endl;
std::list<double> first, second;
first.push_back(3.1);
first.push_back(2.2);
first.push_back(2.9);
second.push_back(3.7);
second.push_back(7.1);
second.push_back(1.4);
first.sort();
second.sort();
first.merge(second);
}
排序时我们使用了一个仿函数，仿函数是一个类可以实现排序时升序还是降序。
merge支持将将两个排序好的链表合并插入到*this中
void test_list5()
{
list<int> lt;
lt.push_back(1);
lt.push_back(20);
lt.push_back(3);
lt.push_back(5);
lt.push_back(5);
lt.push_back(4);
lt.push_back(5);
lt.push_back(6);
lt.sort();
for (auto e : lt)
{
cout << e << " ";
}
cout << endl;
lt.unique();
for (auto e : lt)
{
cout << e << " ";
}
cout << endl;
}
unique实现删除重复元素（在链表排序好的情况下）
void test_list6()
{
// 一个链表节点转移给另一个链表
std::list<int> mylist1, mylist2;
std::list<int>::iterator it;
// set some initial values:
for (int i = 1; i <= 4; ++i)
mylist1.push_back(i); // mylist1: 1 2 3 4
for (int i = 1; i <= 3; ++i)
mylist2.push_back(i * 10); // mylist2: 10 20 30
it = mylist1.begin();
++it; // points to 2
mylist1.splice(it, mylist2); // mylist1: 1 10 20 30 2 3 4
// mylist2 (empty)
// "it" still points to 2 (the 5th element
// 调整当前链表节点的顺序
list<int> lt;
lt.push_back(1);
lt.push_back(2);
lt.push_back(3);
lt.push_back(4);
lt.push_back(5);
lt.push_back(6);
for (auto e : lt)
{
cout << e << " ";
}
cout << endl;
int x = 0;
cin >> x;
it = find(lt.begin(), lt.end(), x);
if (it != lt.end())
{
//lt.splice(lt.begin(), lt, it);
lt.splice(lt.begin(), lt, it, lt.end());
}
for (auto e : lt)
{
cout << e << " ";
}
cout << endl;
}
splice实现粘连可以是一个链表内部的粘连也可以是两个链表去粘连
- 将链表x的所有结点粘连在position之前
- 将链表x中的i结点粘连在position之前
- 将链表x的迭代去区间粘连在position之前
void test_op()
{
srand(time(0));
const int N = 1000000;
list<int> lt1;
list<int> lt2;
for (int i = 0; i < N; ++i)
{
auto e = rand() + i;
lt1.push_back(e);
lt2.push_back(e);
}
int begin1 = clock();
// 拷贝vector
vector<int> v(lt2.begin(), lt2.end());
// 排序
sort(v.begin(), v.end());
// 拷贝回lt2
lt2.assign(v.begin(), v.end());
int end1 = clock();
int begin2 = clock();
lt1.sort();
int end2 = clock();
printf("list copy vector sort copy list sort:%d\n", end1 - begin1);
printf("list sort:%d\n", end2 - begin2);
}
链表排序在算法库中实现，不是类方法的一部分。但是对于链表排序最好把list放到vector中排序在调用assign返回给list，在这样的代价下排序的效率也是远高于对list排序
2.1 模拟实现list
要模拟实现list，必须要熟悉list的底层结构以及其接口的含义，通过上面的学习，这些内容已基本
掌握，现在我们来模拟实现list。
#pragma once
#include<assert.h>
#include<iostream>
using namespace std;
namespace Yusei
{
template<class T>
struct list_node
{
T _date;
list_node<T>* _next;
list_node<T>* _prev;
list_node(const T& date=T())
:_next(nullptr)
,_prev(nullptr)
,_date(date)
{}
};
template<class T, class Ref, class Ptr>
struct list_iterator
{
typedef list_node<T> Node;
typedef list_iterator<T, Ref, Ptr> Self;
Node* _node;
list_iterator(Node* node)
:_node(node)
{}
Ref operator*()
{
return _node->_date;
}
Ptr operator ->()
{
return &_node->_date;
}
Self& operator++()
{
_node=_node->_next;
return *this;
}
Self& operator--()
{
_node = _node->_prev;
return *this;
}
Self& operator++(int)
{
Self tmp(*this);
_node = _node->_next;
return tmp;
}
Self& operator--(int)
{
Self tmp(*this);
_node = _node->_prev;
return tmp;
}
bool operator!=(const Self& s)const
{
return _node != s._node;
}
bool operator==(const Self& s)const
{
return _node == s._node;
}
};
template<class T>
class list
{
typedef list_node<T> Node;
public:
typedef list_iterator<T, T&, T*> iterator;
typedef list_iterator<T, const T&, const T*> const_iterator;
iterator begin()
{
return _head->_next;
}
iterator end()
{
return _head;
}
const_iterator begin() const
{
return _head->_next;
}
const_iterator end() const
{
return _head;
}
void empty_init()
{
_head = new Node;
_head->_next = _head;
_head->_prev = _head;
_size = 0;
}
list()
{
empty_init();
}
list(initializer_list<T> il)
{
empty_init();
for (auto& e : il)
{
push_back(e);
}
}
list(const list<T>& lt)
{
empty_init();
for (auto& e : lt)
{
push_back(e);
}
}
void swap(list<T>& lt)
{
std::swap(_head, lt._head);
std::swap(_size, lt._size);
}
list<T>& operator=(list<T> lt)
{
swap(lt);
return *this;
}
~list()
{
clear();
delete _head;
_head = nullptr;
}
void clear()
{
auto it = begin();
while (it != end())
{
it = erase(it);
}
}
iterator insert(iterator pos, const T& x)
{
Node* cur = pos._node;
Node* prev = cur->_prev;
Node* newnode = new Node(x);
// prev newnode cur
newnode->_next = cur;
cur->_prev = newnode;
newnode->_prev = prev;
prev->_next = newnode;
++_size;
return newnode;
}
void push_back(const T& x)
{
insert(end(), x);
}
void push_front(const T& x)
{
insert(begin(), x);
}
iterator erase(iterator pos)
{
assert(pos != end());
Node* prev = pos._node->_prev;
Node* next = pos._node->_next;
prev->_next = next;
next->_prev = prev;
delete pos._node;
--_size;
return next;
}
void pop_back()
{
erase(--end());
}
void pop_front()
{
erase(begin());
}
size_t size() const
{
return _size;
}
bool empty() const
{
return _size == 0;
}
private:
Node* _head;
size_t _size;
};
struct AA
{
int _a1 = 1;
int _a2 = 1;
};
template<class Container>
void print_container(const Container& con)
{
typename Container::const_iterator it = con.begin();
//auto it = con.begin();
while (it != con.end())
{
//*it += 10;
cout << *it << " ";
++it;
}
cout << endl;
for (auto e : con)
{
cout << e << " ";
}
cout << endl;
}
void test_list1()
{
list<int> lt;
lt.push_back(1);
lt.push_back(2);
lt.push_back(3);
lt.push_back(4);
list<int>::iterator it = lt.begin();
while (it != lt.end())
{
*it += 10;
cout << *it << " ";
++it;
}
cout << endl;
for (auto e : lt)
{
cout << e << " ";
}
cout << endl;
print_container(lt);
list<AA> lta;
lta.push_back(AA());
lta.push_back(AA());
lta.push_back(AA());
lta.push_back(AA());
list<AA>::iterator ita = lta.begin();
while (ita != lta.end())
{
cout << ita->_a1 << ":" << ita->_a2 << endl;
cout << ita.operator->()->_a1 << ":" << ita.operator->()->_a2 << endl;
++ita;
}
cout << endl;
}
void test_list2()
{
list<int> lt;
lt.push_back(1);
lt.push_back(2);
lt.push_back(3);
lt.push_back(4);
// insert以后迭代器不失效
list<int>::iterator it = lt.begin();
lt.insert(it, 10);
*it += 100;
print_container(lt);
// erase以后迭代器失效
// 删除所有的偶数
it = lt.begin();
while (it != lt.end())
{
if (*it % 2 == 0)
{
it = lt.erase(it);
}
else
{
++it;
}
}
print_container(lt);
}
void test_list3()
{
list<int> lt1;
lt1.push_back(1);
lt1.push_back(2);
lt1.push_back(3);
lt1.push_back(4);
list<int> lt2(lt1);
print_container(lt1);
print_container(lt2);
list<int> lt3;
lt3.push_back(10);
lt3.push_back(20);
lt3.push_back(30);
lt3.push_back(40);
lt1 = lt3;
print_container(lt1);
print_container(lt3);
}
void func(const list<int>& lt)
{
print_container(lt);
}
void test_list4()
{
// 直接构造
list<int> lt0({ 1,2,3,4,5,6 });
// 隐式类型转换
list<int> lt1 = { 1,2,3,4,5,6,7,8 };
const list<int>& lt3 = { 1,2,3,4,5,6,7,8 };
func(lt0);
func({ 1,2,3,4,5,6 });
print_container(lt1);
//auto il = { 10, 20, 30 };初始化列表
/* initializer_list<int> il = { 10, 20, 30 };
cout << typeid(il).name() << endl;
cout << sizeof(il) << endl;*/
}
}