18.2.4【STL常用查找算法count】

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


/*
     5.2.5 count
        统计元素个数
        count(iterator beg, iterator end, value);
        // 统计元素出现次数
        // beg 开始迭代器
        // end 结束迭代器
        // value 统计的元素
        统计自定义数据类型时候，需要配合重载 operator==
*/


void test525() //内置数据类型
{
    vector<int> v;
    v.push_back(1);
    v.push_back(2);
    v.push_back(4);
    v.push_back(5);
    v.push_back(2);
    v.push_back(4);
    v.push_back(4);
    v.push_back(3);
    v.push_back(4);

    int num = count(v.begin(), v.end(), 4);
    cout << "num of 4 in v:" << num << endl;
}


class Person
{
public:
    string name;
    int age;

public:
    Person(string _name, int _age)
    {
        this->name = _name;
        this->age = _age;
    }

    bool operator==(const Person & p)
    {
        if(this->age == p.age)
        {
            return true;
        }
        return false;
    }
};


void test525_1() //自定义数据类型
{
    vector<Person> vv;
    Person p1("aaa", 10);
    Person p2("bbb", 20);
    Person p3("ccc", 30);
    Person p4("ddd", 30);
    Person p5("eee", 40);
    Person p6("fff", 30);
    vv.push_back(p1);
    vv.push_back(p2);
    vv.push_back(p3);
    vv.push_back(p4);
    vv.push_back(p5);
    vv.push_back(p6);

    Person p("zzz", 30); //统计vv中跟zzz年龄相同的有多少人
    int num = count(vv.begin(), vv.end(), p);
    cout << "num:" << num << endl;
}


int main()
{
    test525();
    test525_1();

    system("pause");
    return 0;
}