C++常见查找算法-count

C++常见查找算法-count_if

功能描述：

按条件统计元素个数

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

//按条件统计元素个数 #include <iostream> #include <algorithm> #include <string> #include <vector> using namespace std; class Greater4 { public: bool operator()(int val) { return val >= 4; } }; //内置数据类型 void test01() { vector<int> v; v.push_back(1); v.push_back(2); v.push_back(4); v.push_back(5); v.push_back(3); v.push_back(4); v.push_back(4); int num = count_if(v.begin(), v.end(), Greater4()); cout << "大于4的个数为： " << num << endl; } //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 AgeLess35 { public: bool operator()(const Person& p) { return p.m_Age < 35; } }; 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", 20); v.push_back(p1); v.push_back(p2); v.push_back(p3); v.push_back(p4); v.push_back(p5); int num = count_if(v.begin(), v.end(), AgeLess35()); cout << "小于35岁的个数： " << num << endl; } int main() { //test01(); test02(); return 0; } //按值统计count，按条件统计用count_if

C++常见查找算法-count_if