STL常用算法——常用查找算法

自定义类型都要用仿函数判断

1.find()

cpp 复制代码

class Person
{
public:
	Person(string name,int age)
	{
		this->m_Name = name;
		this->m_Age = age;
	}
	bool operator==(const Person &p)//重载operator=
	{
		if (this->m_Name == p.m_Name && this->m_Age == p.m_Age)
		{
			return true;
		}
		return false;
	}
	string m_Name;
	int m_Age;
};
void test01()//find查找内置类型
{
	vector<int> v1;
	v1.push_back(10);
	v1.push_back(20);
	v1.push_back(30);
	v1.push_back(40);
	v1.push_back(50);
	//find查找内置类型
	auto it = find(v1.begin(), v1.end(), 40);//auto自动推出it类型(vector<int>::iterator)
	if (it == v1.end())
	{
		cout << "没找到这个元素" << endl;
	}
	else
	{
		cout << "找到这个元素：" << *it << endl;
	}
}
void test02()find查找自定义类型//类内部要重载operator=
{
	vector<Person> p;
	Person p1("张三", 10);
	Person p2("李四", 15);
	Person p3("王五", 13);
	Person p4("赵六", 16);
	p.push_back(p1);
	p.push_back(p2);
	p.push_back(p3);
	p.push_back(p4);
	Person pf("赵六", 14);
	auto it = find(p.begin(), p.end(), pf);//auto自动推出it类型(vector<int>::iterator)
	if (it == p.end())
	{
		cout << "没找到这个人" << endl;
	}
	else
	{
		cout << "找到了，姓名：" << it->m_Name << " 年龄：" << it->m_Age << endl;
	}
}

2.find_if()

cpp 复制代码

class Person
{
public:
	Person(string name,int age)
	{
		this->m_Name = name;
		this->m_Age = age;
	}
	string m_Name;
	int m_Age;
};
class Greater20//test01
{
public:
	bool operator()(int val)
	{
		return val > 20;
	}
 };
class MyCompare//test02
{
public:
	bool operator()(Person& p)
	{
		return (p.m_Age > 15);
	}
};
void test01()//find_if查找内置类型
{
	vector<int> v1;
	v1.push_back(10);
	v1.push_back(20);
	v1.push_back(30);
	v1.push_back(40);
	v1.push_back(50);
	vector<int>::iterator it=find_if(v1.begin(), v1.end(), Greater20());
	cout << "找到了：" << *it << endl;
}
void test02()find_if查找自定义类型
{
	vector<Person> p;
	Person p1("张三", 10);
	Person p2("李四", 15);
	Person p3("王五", 13);
	Person p4("赵六", 16);
	p.push_back(p1);
	p.push_back(p2);
	p.push_back(p3);
	p.push_back(p4);
	Person pf("赵六", 16);
	vector<Person>::iterator it = find_if(p.begin(), p.end(),MyCompare());
	if (it == p.end())
	{
		cout << "没找到这个人" << endl;
	}
	else
	{
		cout << "找到了，姓名：" << it->m_Name << " 年龄：" << it->m_Age << endl;
	}
}

3.adjacent_find()

cpp 复制代码

void test01()
{
	vector<int> v1;
	v1.push_back(10);
	v1.push_back(20);
	v1.push_back(40);
	v1.push_back(30);
	v1.push_back(40);
	v1.push_back(40);
	v1.push_back(50);
	vector<int>::iterator it = adjacent_find(v1.begin(), v1.end());//查找相邻相同元素
	cout << "找到了：" << *it << endl;
}

4.binary_search()//二分查找

cpp 复制代码

void test01()
{
	vector<int> v1;
	v1.push_back(10);
	v1.push_back(20);
	v1.push_back(40);
	v1.push_back(30);
	v1.push_back(40);
	v1.push_back(40);
	v1.push_back(50);
	sort(v1.begin(), v1.end());//降序不行
	bool ret = binary_search(v1.begin(), v1.end(), 30);
	if (ret)
	{
		cout << "找到了" << endl;
	}
	else
	{
		cout << "没找到" << endl;
	}
}

5.count()

cpp 复制代码

class Person
{
public:
	Person(string name,int age)
	{
		this->m_Name = name;
		this->m_Age = age;
	}
	bool operator==(const Person& p)
	{
		if (this->m_Age == p.m_Age)//按年龄查找年龄相等的人的个数
		{
			return true;
		}
		return false;
	}
	string m_Name;
	int m_Age;
};
void test01()//count查找内置类型
{
	vector<int> v1;
	v1.push_back(10);
	v1.push_back(20);
	v1.push_back(40);
	v1.push_back(30);
	v1.push_back(40);
	v1.push_back(40);
	v1.push_back(50);
	int num = count(v1.begin(), v1.end(), 40);//统计40的个数
	cout << "40的个数是：" << num << endl;

}
void test02()//count查找自定义类型
{
	vector<Person> p;
	Person p1("张三", 10);
	Person p2("李四", 15);
	Person p3("王五", 15);
	Person p4("赵六", 16);
	p.push_back(p1);
	p.push_back(p2);
	p.push_back(p3);
	p.push_back(p4);
	Person pf("张麻子", 15);
	int num = count(p.begin(), p.end(), pf);
	cout << "num=" << num << endl;
}

6.count_if()

cpp 复制代码

class Person
{
public:
	Person(string name,int age)
	{
		this->m_Name = name;
		this->m_Age = age;
	}
	string m_Name;
	int m_Age;
};
class MyCompare
{
public:
	bool operator()(const int val)
	{
		return val > 30;
	}
};
class AgeGreater14
{
public:
	bool operator()(const Person& p)
	{
		return p.m_Age > 14;//统计年龄大于14的人的个数
	}
};
void test01()//count_if统计内置类型
{
	vector<int> v1;
	v1.push_back(10);
	v1.push_back(20);
	v1.push_back(40);
	v1.push_back(30);
	v1.push_back(40);
	v1.push_back(40);
	v1.push_back(50);
	int num = count_if(v1.begin(), v1.end(), MyCompare());//统计大于30的个数
	cout << "大于30的个数是：" << num << endl;

}
void test02()//count_if统计自定义类型
{
	vector<Person> p;
	Person p1("张三", 10);
	Person p2("李四", 14);
	Person p3("王五", 15);
	Person p4("赵六", 16);
	p.push_back(p1);
	p.push_back(p2);
	p.push_back(p3);
	p.push_back(p4);
	int num = count_if(p.begin(), p.end(),AgeGreater15());
	cout << "num=" << num << endl;
}