c++STL之常用查找算法

引入#include<algorithm>

算法简介：

• find：查找元素
• find_if：按条件查找
• adjacent_find：查找相邻房重复的元素
• binary_search：二分查找
• count：统计元素个数
• count_if：按条件统计元素个数

1.find

#include<iostream>
using namespace std;
#include <vector>
#include <algorithm>
#include <string>

//常用查找算法
//find

//查找 内置数据类型
void test01()
{
    vector<int>v;
    for (int i = 0; i < 10; i++)
    {
        v.push_back(i);
    }

    //查找 容器中 是否有 5 这个元素
    vector<int>::iterator it = find(v.begin(), v.end(), 5);
    if (it == v.end())
    {
        cout << "没有找到！" << endl;
    }
    else
    {
        cout << "找到： " << *it << endl;
    }
}


class Person
{
public:
    Person(string name, int age)
    {
        this->m_Name = name;
        this->m_Age = age;
    }

    //重载 ==  底层find知道如何对比person数据类型
    bool operator==( const Person & p)
    {
        if (this->m_Name == p.m_Name && this->m_Age == p.m_Age)
        {
            return true;
        }
        else
        {
            return false;
        }
    }
    string m_Name;
    int m_Age;
};

//查找 自定义数据类型
void test02()
{
    vector<Person>v;
    //创建数据
    Person p1("aaa", 10);
    Person p2("bbb", 20);
    Person p3("ccc", 30);
    Person p4("ddd", 40);

    //放入到容器中
    v.push_back(p1);
    v.push_back(p2);
    v.push_back(p3);
    v.push_back(p4);

    Person pp("bbb", 20);

    vector<Person>::iterator it = find(v.begin(), v.end(), pp);
    if (it == v.end())
    {
        cout << "没有找到" << endl;
    }
    else
    {
        cout << "找到元素  姓名：" << it->m_Name << " 年龄： " << it->m_Age << endl;
    }
}

int main() {

    //test01();

    test02();

    system("pause");

    return 0;
}

2.find_if

#include<iostream>
using namespace std;
#include <vector>
#include <algorithm>
#include <string>
//常用查找算法 find_if

//1、查找内置数据类型
class GreaterFive
{
public:
    bool operator()(int val)
    {
        return val > 5;
    }
};

void test01()
{
    vector<int>v;
    for (int i = 0; i < 10; i++)
    {
        v.push_back(i);
    }

    vector<int>::iterator it = find_if(v.begin(), v.end(), GreaterFive());

    if (it == v.end())
    {
        cout << "没有找到" << endl;
    }
    else
    {
        cout << "找到大于5的数字为： " << *it << endl;
    }

}

//2、查找自定义数据类型
class Person
{
public:
    Person(string name, int age)
    {
        this->m_Name = name;
        this->m_Age = age;
    }
    string m_Name;
    int m_Age;
};

class Greater20
{
public:
    bool operator()(Person &p)
    {
        return  p.m_Age > 20;
    }
};

void test02()
{
    vector<Person>v;

    //创建数据
    Person p1("aaa", 10);
    Person p2("bbb", 20);
    Person p3("ccc", 30);
    Person p4("ddd", 40);

    v.push_back(p1);
    v.push_back(p2);
    v.push_back(p3);
    v.push_back(p4);

    //找年龄大于20的人
    vector<Person>::iterator it = find_if(v.begin(), v.end(), Greater20());

    if (it == v.end())
    {
        cout << "没有找到" << endl;
    }
    else
    {
        cout << "找到姓名： " << it->m_Name << " 年龄： " << it->m_Age << endl;
    }
}

int main() {

    //test01();

    test02();

    system("pause");

    return 0;
}

3.adjacent_find

#include<iostream>
using namespace std;
#include <vector>
#include <algorithm>

//常用查找算法 adjacent_find
void test01()
{
    vector<int>v;
    v.push_back(0);
    v.push_back(2);
    v.push_back(0);
    v.push_back(3);
    v.push_back(1);
    v.push_back(4);
    v.push_back(3);
    v.push_back(3);

    vector<int>::iterator  pos = adjacent_find(v.begin(), v.end());
 
    if (pos == v.end())
    {
        cout << "未找到相邻重复元素" << endl;
    }
    else
    {
        cout << "找到相邻重复元素：" << *pos << endl;
    }

}

int main() {

    test01();

    system("pause");

    return 0;
}

4.binary_search

#include<iostream>
using namespace std;
#include <vector>
#include <algorithm>

//常用查找算法 binary_search
void test01()
{
    vector<int>v;
    for (int i = 0; i < 10; i++)
    {
        v.push_back(i);
    }
    //v.push_back(2);  如果是无序序列，结果未知！
    //查找容器中是否有9 元素
    //注意：容器必须是有序的序列
    bool ret = binary_search(v.begin(), v.end(), 9);

    if (ret)
    {
        cout << "找到了元素" << endl;
    }
    else
    {
        cout << "未找到" << endl;
    }
}

int main() {

    test01();

    system("pause");

    return 0;
}

5.count

#include<iostream>
using namespace std;
#include <vector>
#include <algorithm>
#include <string>
//常用查找算法_count

//1、统计内置数据类型

void test01()
{
    vector<int>v;

    v.push_back(10);
    v.push_back(40);
    v.push_back(30);
    v.push_back(40);
    v.push_back(20);
    v.push_back(40);

    int num = count(v.begin(), v.end(), 40);

    cout << "40的元素个数为： " << num << endl;
}

//2、统计自定义数据类型

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)
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    string m_Name;
    int m_Age;
};

void test02()
{
    vector<Person>v;

    Person p1("刘备", 35);
    Person p2("关羽", 35);
    Person p3("张飞", 35);
    Person p4("赵云", 30);
    Person p5("曹操", 40);

    //将人员插入到容器中
    v.push_back(p1);
    v.push_back(p2);
    v.push_back(p3);
    v.push_back(p4);
    v.push_back(p5);

    Person p("诸葛亮", 35);

    int num = count(v.begin(), v.end(), p);

    cout << "和诸葛亮同岁数的人员个数为：" << num << endl;
}

int main() {
    
    //test01();

    test02();

    system("pause");

    return 0;
}

6.count_if

#include<iostream>
using namespace std;
#include <vector>
#include <algorithm>

//常用查找算法  count_if

//统计内置数据类型
class Greater20
{
public:
    bool operator()(int val)
    {
        return val > 20;
    }
};

void test01()
{
    vector<int>v;
    v.push_back(10);
    v.push_back(40);
    v.push_back(30);
    v.push_back(20);
    v.push_back(40);
    v.push_back(20);

    int num = count_if(v.begin(), v.end(), Greater20());

    cout << "大于20的元素个数为： " << num << endl;
}

class Person
{
public:
    Person(string name, int age)
    {
        this->m_Name = name;
        this->m_Age = age;
    }
    string m_Name;
    int m_Age;
};

class AgeGreater20
{
public:
    bool operator()(const Person& p)
    {
        return p.m_Age > 20;
    }
};

//统计自定义数据类型
void test02()
{
    vector<Person>v;

    Person p1("刘备", 35);
    Person p2("关羽", 35);
    Person p3("张飞", 35);
    Person p4("赵云", 40);
    Person p5("曹操", 20);

    v.push_back(p1);
    v.push_back(p2);
    v.push_back(p3);
    v.push_back(p4);
    v.push_back(p5);

    //统计  大于20岁人员个数
    int num = count_if(v.begin(), v.end(), AgeGreater20());
    cout << "大于20岁的人员个数为：" << num << endl;
}

int main() {

    //test01();

    test02();

    system("pause");

    return 0;
}