C++ --STL的常用算法

文章目录

• STL的常用算法
• 一、遍历
• 二、查找
• • 2.1 find, find_if
  • 2.2 adjacent_find
  • 2.3 binary_search
  • 2.4 count, count_if

STL的常用算法 一、遍历

• for_each
• transform

//遍历算法：for_each, transform
#include 
#include 
class Traversing
{
public:
	void operator()(int v)
	{
		cout << v << " ";
	}
};
class Transform
{
public:
	int operator()(int v)
	{
		return v + 100;
	}
};
void test()
{
	vector<int> v;
	for (int i = 0; i < 10; i++)
	{
		v.push_back(i + 20);
	}
	//遍历vector容器 for_each
	for_each(v.begin(), v.end(), Traversing());			//函数对象，Traversing()
	cout << endl;

	//transform遍历加转换
	vector<int> v2;
	v2.resize(10);
	transform(v.begin(), v.end(), v2.begin(), Transform());			//函数对象，Transform()
	for_each(v2.begin(), v2.end(), Traversing());
}
int main()
{
	test();
	return 0;
}

二、查找

• find find_if
• adjacent_find
• binary_search
• count count_if

2.1 find, find_if

//find   返回值是一个迭代器，如果没找到返回 .end()迭代器
//find_if  条件查找，同样返回一个迭代器，没找到就返回end()迭代器
#include 
#include 
class Person
{
public:
	string name;
	int age;
	Person(string s, int a) : name(s), age(a) {}
	bool operator==(const Person& p)
	{
		if (this->name == p.name && this->age == p.age)
		{
			return true;
		}
		else
		{
			return false;
		}
	}
};
class GreaterT
{
public:
	bool operator()(Person& p)
	{
		return p.age > 25;
	}
};
void test()
{
	vector<Person> v;
	Person p1("xwp", 26);
	Person p2("yjj", 25);
	Person p3("xxz", 21);
	v.push_back(p1);
	v.push_back(p2);
	v.push_back(p3);
	Person p4("xwp", 18);
	Person p5("yjj", 25);
	vector<Person>::iterator it;
	it = find(v.begin(), v.end(), p5);			//find会对对象进行 == 判断，所以如果是自定义的类，需要重载 ==
	if (it == v.end())
	{
		cout << "未找到\n";
	}
	else
	{
		cout << "找到了\n";
	}
	v.push_back(p4);
	v.push_back(p5);
	it = find_if(v.begin(), v.end(), GreaterT());				//Greater()，谓词
	if (it == v.end())
	{
		cout << "未找到\n";
	}
	else
	{
		cout << "找到了 " << it->name << " " << it->age << endl;
	}
}
int main()
{
	test();
	return 0;
}

2.2 adjacent_find

//adjacent_find
//查找相邻的重复元素，没找到返回迭代器end()

2.3 binary_search

//binary_search   二分查找，极快
//返回bool，只能用于有序序列
#include 
#include 
void test()
{
	vector<int> v;
	v.push_back(2);
	v.push_back(3);
	v.push_back(22);
	v.push_back(11);
	sort(v.begin(), v.end());		//排序
	bool result = binary_search(v.begin(), v.end(), 11);
	cout << result << endl;
}
int main()
{
	test();
	return 0;
}

2.4 count, count_if

//count  统计元素出现的次数
//count_if   按条件统计
#include 
#include 
class Greater23
{
public:
	bool operator()(int val)
	{
		return val > 23;
	}
};
void test()
{
	vector<int> v;
	v.push_back(20);
	v.push_back(20);
	v.push_back(30);
	v.push_back(20);
	v.push_back(25);
	int result = count(v.begin(), v.end(), 20);
	cout << "20出现的次数：" << result << endl;
	int result2 = count_if(v.begin(), v.end(), Greater23());
	cout << "大于23的数字个数：" << result2 << endl;
}
int main()
{
	test();
	return 0;
}