C++——list

1.简介

list：带头双向循环链表

2.遍历方式

void test_list1()
{
	list<int> lt;
	lt.push_back(1);
	lt.push_back(2);
	lt.push_back(3);
	lt.push_back(4);
	lt.push_back(5);

	//遍历方式，不再支持[]
    //当然是可以支持的，但效率过低
	list<int>::iterator it = lt.begin();

    //迭代器是属于内嵌类型，一般使用typedef或是内部类的方式实现
    //list的迭代器更加复杂，就不是原生指针了

	while (it != lt.end())
	{
		cout << *(it++) << " ";
	}
	cout << endl;

	//底层就是迭代器，编译会器把范围for替换成迭代器
	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;
}

3.构造

4. Modifiers

4.1 assign

4.2 insert

5. Operations

5.1 reverse

void test_list2()
{
	list<int> lt;
	lt.push_back(1);
	lt.push_back(2);
	lt.push_back(3);
	lt.push_back(4);
	lt.push_back(5);

	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;


	lt.reverse();//逆置

	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;

}

5.2 sort

为什么算法库中有sort ，list还要单独写个sort

算法库的sort

list的sort

void test_list2()
{
	list<int> lt;
	lt.push_back(5);
	lt.push_back(4);
	lt.push_back(3);
	lt.push_back(2);
	lt.push_back(1);

	//sort(lt.begin(), lt.end());//使用时要包含头文件<algorithm>


	lt.sort();//默认是升序

	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;

	//升序 < less

	//如果想排降序 > greater
	// 1.
	//greater<int> gt;
	//lt.sort(gt);

	//2.
	lt.sort(greater<int>());//使用匿名对象

	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;

}

5.2.1比较库中与list中sort的性能差异

//注意：测试性能时要切换为release
void test_op()
{
	srand(time(0));
	const int N = 100000;

	vector<int> v;
	list<int> lt1;

	for (int i = 0; i < N; ++i)
	{
		auto e = rand();
		lt1.push_back(e);
		v.push_back(e);
	}

	//1.库中的sort
	int begin1 = clock();
	sort(v.begin(),v.end());
	int end1 = clock();

	//2.list的sort
	int begin2 = clock();
	lt1.sort();
	int end2 = clock();

	printf("vector sort:%d\n", end1 - begin1);
	printf("list sort:%d\n", end2 - begin2);
}

结论：库中的sort性能更好

//实际上，list的排序是很无用的
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();
		lt1.push_back(e);
		lt2.push_back(e);
	}

	//
	int begin1 = clock();

	//1.先拷贝到vector
	vector<int> v(lt2.begin(),lt2.end());

	//2.排序
	sort(v.begin(),v.end());

	//3.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);
    //哪怕是这样，库中的sort性能也更好
    //也说明了拷贝数据的代价并没有很大
	printf("list sort:%d\n", end2 - begin2);
}

list中sort的优势就是方便一些，数据量少时可以使用

5.3 merge

5.4 unique

void test_list3()
{
	list<int> lt;
	lt.push_back(1);
	lt.push_back(2);
	lt.push_back(2);
	lt.push_back(2);
	lt.push_back(3);
	lt.push_back(4);
	lt.push_back(5);
	lt.push_back(5);
	lt.push_back(5);

	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;

	lt.unique();

	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;
}

5.5 remove

void test_list3()
{
	list<int> lt;
	lt.push_back(1);
	lt.push_back(2);
	lt.push_back(2);
	lt.push_back(2);
	lt.push_back(3);
	lt.push_back(4);
	lt.push_back(5);
	lt.push_back(5);
	lt.push_back(5);

	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;

	lt.remove(2);
	lt.remove(30);
	//如果remove一个不存在的值，就什么也不会做
	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;
}

5.6 splice

void test_list4()
{
	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

	for (auto e : mylist1)
	{
		cout << e << " ";
	}
	cout << endl;

	for (auto e : mylist2)
	{
		cout << e << " ";
	}
	cout << endl;

	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)

	for (auto e : mylist1)
	{
		cout << e << " ";
	}
	cout << endl;

	for (auto e : mylist2)
	{
		cout << e << " ";
	}
	cout << endl;
}