c++常用stl算法
1、头文件
这些算法通常包含在头文件
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 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 &v) {
for (auto i : v) {
cout << i << " ";
}
cout << endl;
}
int main() {
vector vi(10, 3);
vector 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 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::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 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::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;
else
return false;
}
};
int main() {
vector 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::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 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;
else
return false;
}
};
int main() {
vector 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 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 vi1{ 1,2,3,4,5 };
vector vi2{ 2,3,4,5,7 };
vector 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 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 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 target;
target.resize(v.size());
copy(v.begin(), v.end(), target.begin()); replace元素替换
vector 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;
else
return false;
}
};
int main() {
vector 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 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
