c++常用stl算法

1、头文件

        这些算法通常包含在头文件<algorithm> <functional> <numeric>中。

 2、常用遍历算法

for_each(v.begin(),v.end(), 元素处理函数/仿函数) 

注意：在使用transform转存时，目标容器需要提取开辟合适的空间。 

void printfunc(int val) {cout << val << " ";
}
class Printoperator {
public:void operator()(int val) {cout << val << " ";}
};
int main() {vector<int> vi(10, 3);//输入一般函数完成for_each算法中的元素处理for_each(vi.begin(), vi.end(), printfunc);cout << endl;//输入仿函数完成for_each算法中的元素处理for_each(vi.begin(), vi.end(), Printoperator());cout << endl;system("pause");return 0;
}

class Printoperator {
public:int operator()(int val) {return val + 1;}
};
void print(vector<int> &v) {for (auto i : v) {cout << i << " ";}cout << endl;
}
int main() {vector<int> vi(10, 3);vector<int> vi2(4, 5);//需要提前给目标容器开辟空间,不然会报错vi2.resize(vi.size());transform(vi.begin(), vi.end(), vi2.begin(), Printoperator());print(vi2);system("pause");return 0;
}

3、常用查找算法

 find按值查找元素

函数原型：

         使用find查找自定义类型元素的时候，需要在对应类中重载==，以便find算法能知道该怎么比较。

class Person {
public:Person(int age, string name) {this->mAge = age;this->mName = name;}//帮助find查找元素bool operator==(const Person &p) {if (p.mAge == this->mAge && p.mName == this->mName) {return true;}else {return false;}}int mAge;string mName;
};
int main() {vector<Person> v;Person p1(10, "aaa");Person p2(20, "sss");Person p3(40, "ads");Person p4(10, "ccc");v.push_back(p1);v.push_back(p2);v.push_back(p3);v.push_back(p4);vector<Person>::iterator iter = find(v.begin(), v.end(), p2);if (iter != v.end()) {cout << "逮到 ！！！" << endl;}system("pause");return 0;
}

 find_if按值查找元素

         利用find_if按自定义谓词找到合适的自定义类型元素：

class Person {
public:Person(int age, string name) {this->mAge = age;this->mName = name;}int mAge;string mName;
};
class FindPerson {
public:bool operator()(const Person &p) {return p.mAge > 20;}
};
int main() {vector<Person> v;Person p1(10, "aaa");Person p2(20, "sss");Person p3(40, "ads");Person p4(10, "ccc");v.push_back(p1);v.push_back(p2);v.push_back(p3);v.push_back(p4);vector<Person>::iterator iter = find_if(v.begin(), v.end(), FindPerson());if (iter != v.end()) {cout << (*iter).mName<<" 的年龄超过了20" << endl;}system("pause");return 0;
}

adjacent_find查找相邻重复元素 

         adjacen_find按自定义谓词查找相邻满足条件自定义元素：

class Person {
public:Person(int age, string name) {this->mAge = age;this->mName = name;}int mAge;string mName;
};
class FindPerson {
public:bool operator()(const Person &p1, const Person& p2) {if (p1.mAge == p2.mAge)return true;elsereturn false;}
};
int main() {vector<Person> v;Person p1(10, "aaa");Person p2(20, "sss");Person p3(20, "sad");Person p4(40, "ads");Person p5(10, "ccc");v.push_back(p1);v.push_back(p2);v.push_back(p3);v.push_back(p4);v.push_back(p5);vector<Person>::iterator iter = adjacent_find(v.begin(), v.end(), FindPerson());if (iter != v.end()) {cout <<"有相邻年龄相同的人" << (*iter).mName <<"和" << (*(iter+1)).mName << endl;}else {cout << "没有相邻年龄相同的人" << endl;}system("pause");return 0;
}

binary_search查指定元素是否存在（不适用无序序列，必须有序且为升序序列） 

count统计元素出现次数

返回int

class Person {
public:Person(int age, string name) {this->mAge = age;this->mName = name;}//帮助count查找元素bool operator==(const Person &p) {if (p.mAge == this->mAge) {return true;}else {return false;}}int mAge;string mName;
};int main() {vector<Person> v;Person p1(10, "aaa");Person p2(20, "sss");Person p3(20, "sad");Person p4(40, "ads");Person p5(10, "ccc");v.push_back(p1);v.push_back(p2);v.push_back(p3);v.push_back(p4);v.push_back(p5);int num = count(v.begin(), v.end(), p2);cout << "20岁的人有 " << num << "个"  << endl;system("pause");return 0;
}

count_if 按条件统计元素个数 ，返回int

count_if的谓词使用参见find_if。 

4、常用排序算法

        

 sort排序

 对自定义类型排序：

class Person {
public:Person(int age, string name) {this->mAge = age;this->mName = name;}int mAge;string mName;
};
class SortPerson {
public:bool operator()(const Person& p1, const Person& p2) {if (p1.mAge > p2.mAge)return true;elsereturn false;}
};
int main() {vector<Person> v;Person p1(10, "aaa");Person p2(20, "sss");Person p3(20, "sad");Person p4(40, "ads");Person p5(10, "ccc");v.push_back(p1);v.push_back(p2);v.push_back(p3);v.push_back(p4);v.push_back(p5);sort(v.begin(), v.end(), SortPerson());system("pause");return 0;
}

random_shuffle随机调序 

int main() {vector<Person> v;Person p1(10, "aaa");Person p2(20, "sss");Person p3(20, "sad");Person p4(40, "ads");Person p5(10, "ccc");v.push_back(p1);v.push_back(p2);v.push_back(p3);v.push_back(p4);v.push_back(p5);random_shuffle(v.begin(), v.end());//cout << "20岁的人有 " << num << "个"  << endl;system("pause");return 0;
}

 

 merge合并容器元素（容器必须有序，提取个目标容器分配空间）

	vector<int> vi1{ 1,2,3,4,5 };vector<int> vi2{ 2,3,4,5,7 };vector<int> target;//提前个target开辟空间target.resize((vi1.size() + vi2.size()));merge(vi1.begin(), vi1.end(), vi2.begin(), vi2.end(),target.begin());

reverse反转容器中的元素 （不需要谓词就能实现自定义类型反转）

 

	vector<Person> v;Person p1(10, "aaa");Person p2(20, "sss");Person p3(20, "sad");Person p4(40, "ads");Person p5(10, "ccc");v.push_back(p1);v.push_back(p2);v.push_back(p3);v.push_back(p4);v.push_back(p5);reverse(v.begin(), v.end());

5、常用拷贝替换生成算法

copy拷贝（需要预先开辟空间）

注：在拷贝自定义类时，需要有对应的空默认构造函数，如：Person(){}。 

	vector<Person> v;Person p1(10, "aaa");Person p2(20, "sss");Person p3(20, "sad");Person p4(40, "ads");Person p5(10, "ccc");v.push_back(p1);v.push_back(p2);v.push_back(p3);v.push_back(p4);v.push_back(p5);vector<Person> target;target.resize(v.size());copy(v.begin(), v.end(), target.begin());

replace元素替换

	vector<int> vi1{ 1,2,3,4,5 };replace(vi1.begin(), vi1.end(), 1, 20);

replace_if满足条件元素替换

class Person {
public:Person() {}Person(int age, string name) {this->mAge = age;this->mName = name;}int mAge;string mName;
};class ReplacePerson {
public:bool operator()(const Person& p) {if (p.mAge > 20)return true;elsereturn false;}
};
int main() {vector<Person> v;Person p1(10, "aaa");Person p2(20, "sss");Person p3(20, "sad");Person p4(40, "ads");Person p5(10, "ccc");v.push_back(p1);v.push_back(p2);v.push_back(p3);v.push_back(p4);v.push_back(p5);Person p6(10, "dsaf");replace_if(v.begin(), v.end(), ReplacePerson(), p6);system("pause");return 0;
}

swap交换容器元素

 6、常用算术生成算法

accumulate计算累加

 

对自定义类型的某成员变量累加：（也可以采用仿函数形式）

class Person {
public:Person() {}Person(int age, string name) {this->mAge = age;this->mName = name;}int mAge;string mName;
};int Age_acc(int pre,Person& p) {return pre + p.mAge;
}
int main() {vector<Person> v;Person p1(10, "aaa");Person p2(20, "sss");Person p3(20, "sad");Person p4(40, "ads");Person p5(10, "ccc");v.push_back(p1);v.push_back(p2);v.push_back(p3);v.push_back(p4);v.push_back(p5);Person p6(10, "dsaf");int acu = accumulate(v.begin(), v.end(), 0, Age_acc);system("pause");return 0;
}

 fill向容器中填充元素

 7、常用集合算法

 set_intersection求两个容器交集（必须预先开辟目标容器空间）

set_union求两个容器并集

set_difference求两个容器差集