算法简介：

• find ——//查找元素
• find_if ——//按条件查找元素
• adjacent_find ——//查找相邻重复元素
• binary_search ——//二分查找法
• count ——//统计元素个数
• count_if ——//按条件统计元素个数

1.find

函数原型：

• find(iterator beg, iterator end, value);——// 按值查找元素，找到返回指定位置迭代器，找不到返回结束迭代器位置；beg 开始迭代器；end 结束迭代器；value 查找的元素

#include<iostream>
using namespace std;
#include<vector>
#include<algorithm>
#include<string>
//find——查找算法
//查找内置数据类型
void test01()
{vector<int>v;for (int i = 0; i < 10; i++){v.push_back(i);}vector<int>::iterator it = find(v.begin(), v.end(), 5);if (it == v.end()){cout << "没有找到！" << endl;}else{cout << "找到了：" << *it << endl;}
}
//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;}//重载 == 让底层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;
};
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);Person p5("eee", 50);//导入数据v.push_back(p1);v.push_back(p2);v.push_back(p3);v.push_back(p4);v.push_back(p5);Person pp("ccc", 30);vector<Person>::iterator it = find(v.begin(), v.end(), pp);if (it == v.end()){cout << "没有找到！" << endl;}else{cout << "找到了：name = " << (*it).m_name << " age = " << it->m_age << endl;}
}
int main()
{//test01();test02();system("pause");return 0;
}

2.find_if

函数原型：

• find_if(iterator beg, iterator end, _Pred);——// 按值查找元素，找到返回指定位置迭代器，找不到返回结束迭代器位置；beg 开始迭代器；end 结束迭代器； _Pred 函数或者谓词（返回bool类型的仿函数）

#include<iostream>
using namespace std;
#include<vector>
#include<algorithm>
//find_if——查找算法
class GreatFive
{
public:bool operator ()(int val){if (val > 5){return true;}else{return false;}}
};
//查找内置数据类型
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(), GreatFive());if (it == v.end()){cout << "没有找到大于5的数：" << endl;}else{cout << "找到了：" << *it << endl;}
}
//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 Great20
{
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);//插入数据v.push_back(p1);v.push_back(p2);v.push_back(p3);v.push_back(p4);//找年龄大于20岁的人vector<Person>::iterator it = find_if(v.begin(), v.end(), Great20());if (it == v.end()){cout << "没有找到！" << endl;}else{cout << "找到了：name = " << it->m_name << " age = " << it->m_age << endl;}
}
int main()
{//test01();test02();system("pause");return 0;
}

3.adjacent_find

函数原型:

• adjacent_find(iterator beg, iterator end);——// 查找相邻重复元素,返回相邻元素的第一个位置的迭代器；beg 开始迭代器；end 结束迭代器

#include<iostream>
using namespace std;
#include<vector>
#include<algorithm>
//adjacent_find——查找相邻重复元素
void test01()
{vector<int>v;v.push_back(1);v.push_back(5);v.push_back(3);v.push_back(9);v.push_back(6);v.push_back(6);v.push_back(8);v.push_back(3);vector<int>::iterator pos = adjacent_find(v.begin(), v.end());if (pos == v.end()){cout << "没有相邻重复元素！" << endl;}else{cout << "找到了相邻重复元素：" << *pos << endl;}
}
int main()
{test01();system("pause");return 0;
}

4.binary_search

函数原型：

• bool binary_search(iterator beg, iterator end, value);——// 查找指定的元素，查到 返回true 否则false；注意: 在无序序列中不可用； beg 开始迭代器； end 结束迭代器；value 查找的元素

#include<iostream>
using namespace std;
#include<vector>
#include<algorithm>
//binary_search——查找容器中指定元素是否存在（有序序列）
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：容器必须是有序序列bool ret = binary_search(v.begin(), v.end(), 9);if (ret){cout << "找到了！" << endl;}else{cout << "没有找到！" << endl;}
}
int main()
{test01();system("pause");return 0;
}

注：二分查找法效率很高，但查找容器中元素必须为有序序列。

5.count

函数原型：

• 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

#include<iostream>
using namespace std;
#include<vector>
#include<algorithm>
//count——查找算法
//查找内置数据类型
void test01()
{vector<int>v;v.push_back(20);v.push_back(50);v.push_back(90);v.push_back(40);v.push_back(50);v.push_back(80);v.push_back(50);int num = count(v.begin(), v.end(), 50);cout << "容器中5的个数为：" << num << endl;
}
//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;}bool operator ==(const Person &p){if (p.m_age == this->m_age){return true;}else{return false;}}string m_name;int m_age;
};
void test02()
{vector<Person>v;//创建数据Person p1("aaa", 25);Person p2("bbb", 45);Person p3("ccc", 25);Person p4("ddd", 60);Person p5("eee", 25);Person p6("fff", 16);Person p7("ggg", 25);//导入数据v.push_back(p1);v.push_back(p2);v.push_back(p3);v.push_back(p4);v.push_back(p5);v.push_back(p6);v.push_back(p7);Person c("compare", 25);int num = count(v.begin(), v.end(), c);cout << "与compare年龄相同的人个数：" << num << endl;
}
int main()
{//test01();test02();system("pause");return 0;
}

注：统计自定义数据类型时需要配合重载operator==

6.count_if

函数原型：

• count_if(iterator beg, iterator end, _Pred);——// 按条件统计元素出现次数；beg 开始迭代器；end 结束迭代器； _Pred 谓词

#include<iostream>
using namespace std;
#include<vector>
#include<algorithm>
#include<functional>
//count_if——条件查找
//查找内置数据类型
class Greater30
{
public:bool operator()(int val){return val > 30;}
};
void test01()
{vector<int>v;v.push_back(10);v.push_back(50);v.push_back(80);v.push_back(60);v.push_back(30);v.push_back(40);//查找大于30的数的个数int num = count_if(v.begin(), v.end(), Greater30());cout << "大于30的数的个数：" << num << endl;
}
//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 ageGreater18
{
public:bool operator()(Person& p){return p.m_age > 18;}
};
void test02()
{vector<Person>v;//创建数据Person p1("aaa", 15);Person p2("bbb", 45);Person p3("ddd", 18);Person p4("fff", 60);Person p5("jjj", 85);//导入数据v.push_back(p1);v.push_back(p2);v.push_back(p3);v.push_back(p4);v.push_back(p5);//查找年龄大于18的人的个数int num = count_if(v.begin(), v.end(), ageGreater18());cout << "年龄大于18的人数：" << num << endl;
}
int main()
{//test01();test02();system("pause");return 0;
}