概述
算法主要是由头文件<algotithm>,<functional>,<numeric>组成,其中<algorithm>头文件最为常见
1.常用的遍历算法for_each和transform
for_each函数原型:
for_each(iterator beg,iterator end,_func)
//beg 开始迭代器
//end 结束迭代器
//_func 函数或者函数对象(仿函数)
例:
void print01(int v)
{
cout << v << " ";
}
class print02
{
public:
void operator()(int c)
{
cout << c << " ";
}
};
int main()
{
vector<int>v;
for (int i = 0; i < 10; i++)
v.push_back(i);
for_each(v.begin(), v.end(), print01);//传入函数
cout << endl;
for_each(v.begin(), v.end(), print02());//传入函数对象
return 0;
}
transform函数原型:
transform(iterator beg1,iterator end1,iterator beg2,_func)
//beg1 源容器开始迭代器
//end1 源容器结束迭代器
//beg2 目标容器开始迭代器
//_func 函数或者函数对象
例:
class print02
{
public:
void operator()(int c)
{
cout << c << " ";
}
};
class Transform
{
public:
int operator()(int c)
{
return c;
}
};
int main()
{
vector<int>v;
for (int i = 0; i < 10; i++)
v.push_back(i);
vector<int>v2;
v2.resize(v.size());
transform(v.begin(), v.end(), v2.begin(), Transform());
for_each(v2.begin(), v2.end(), print02());
cout << endl;
return 0;
}
2.常用查找算法
find函数
原型
find(iterator beg,iterator end,value)
//按值查找元素,找到返回指定位置的迭代器,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
例:
查找自定义数据类型,要重载==运算符,这样find函数知道该如何比较
class Person
{
public:
Person(string name,int age)
{
m_name = name;
m_age = age;
}
bool operator ==(const Person&p)
{
if (this->m_age == p.m_age && this->m_name == p.m_name)
return true;
else
return false;
}
string m_name;
int m_age;
};
int main()
{
vector<int>v;
for (int i = 0; i < 10; i++)
v.push_back(i);
vector<int>::iterator it = find(v.begin(), v.end(), 4);
if (it != v.end())
cout << "找到元素:" << *it << endl;
else
cout << "没有找到元素" << endl;
//查找自定义数据类型
vector<Person>v2;
Person p1("aaa", 111);
Person p2("bbb", 222);
Person p3("ccc", 333);
Person p4("ddd", 444);
v2.push_back(p1);
v2.push_back(p2);
v2.push_back(p3);
v2.push_back(p4);
vector<Person>::iterator IT = find(v2.begin(), v2.end(),p2);
if (IT != v2.end())
cout << "找到元素:" << IT->m_name<<" "<<IT->m_age<< endl;
else
cout << "没有找到元素" << endl;
return 0;
}
find_if函数
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(bool类型的仿函数)
class Person
{
public:
Person(string name,int age)
{
m_name = name;
m_age = age;
}
string m_name;
int m_age;
};
class Compare
{
public:
bool operator()(int val)
{
return val > 5;
}
};
class Compare2
{
public:
bool operator()(Person&p)
{
return p.m_age > 300;
}
};
int main()
{
vector<int>v;
for (int i = 0; i < 10; i++)
v.push_back(i);
vector<int>::iterator it = find_if(v.begin(), v.end(), Compare());
if (it != v.end())
cout << "找到元素:" << *it << endl;
else
cout << "没有找到元素" << endl;
//查找自定义数据类型
vector<Person>v2;
Person p1("aaa", 111);
Person p2("bbb", 222);
Person p3("ccc", 333);
Person p4("ddd", 444);
v2.push_back(p1);
v2.push_back(p2);
v2.push_back(p3);
v2.push_back(p4);
vector<Person>::iterator IT = find_if(v2.begin(), v2.end(),Compare2());
if (IT != v2.end())
cout << "找到元素:" << IT->m_name<<" "<<IT->m_age<< endl;
else
cout << "没有找到元素" << endl;
return 0;
}
adjacent_find函数
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
int main()
{
vector<int>v;
for (int i = 0; i <=10; i++)
v.push_back(i);
v.push_back(10);
vector<int>::iterator it = adjacent_find(v.begin(), v.end());
if (it != v.end())
cout << "找到有相邻重复元素,为:" << *it << endl;
else
cout << "没有找到" << endl;
return 0;
}
binary_search函数
bool binary_search(iterator beg,iterator end,value)
//查找指定的元素,查到返回true,否则false
//beg 开始迭代器
//end 结束迭代器
//value 查找的元素
!!!注意:binary_search函数一定是在有序序列中查找,不能在无序序列进行查找
int main()
{
vector<int>v;
for (int i = 0; i < 10; i++)
v.push_back(i);
bool res = binary_search(v.begin(), v.end(), 4);
if (res)
cout << "找到了" << endl;
else
cout << "没有找到元素" << endl;
return 0;
}
count函数
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
class Person
{
public:
Person(string name, int age)
{
m_name = name;
m_age = age;
}
bool operator==(const Person& p)
{
if (this->m_age == p.m_age)
return true;
else
return false;
}
string m_name;
int m_age;
};
int main()
{
vector<int>v;
for (int i = 0; i < 10; i++)
v.push_back(i);
int num = count(v.begin(), v.end(), 8);
cout << "统计8的个数为:" << num << endl;
//统计自定义类型的个数,需要重载==运算符
vector<Person>v2;
Person p1("张飞", 35);
Person p2("刘备",30);
Person p3("关羽", 35);
Person p4("孙尚香", 20);
Person p5("孙权", 25);
v2.push_back(p1);
v2.push_back(p2);
v2.push_back(p3);
v2.push_back(p4);
v2.push_back(p5);
num = count(v2.begin(), v2.end(),p1);
cout << "统计年龄和张飞一样的总人数为:" << num << endl;
return 0;
}
count_if函数
count_if(iterator beg,iterator end,_Pred)
//按条件统计元素出现个数
//beg 开始迭代器
//end 结束迭代器
//_Pred 谓词
class Compare
{
public:
bool operator()(int val)
{
return val > 4;
}
};
void test01()
{
vector<int>v;
for (int i = 0; i < 10; i++)
v.push_back(i);
int num = count_if(v.begin(), v.end(), Compare());
cout << "大于4的统计个数为:" << num << endl;
}
class Person
{
public:
Person(string name, int age)
{
m_name = name;
m_age = age;
}
string m_name;
int m_age;
};
class Compare2
{
public:
bool operator()(const Person& p)
{
if (p.m_age>22)
return true;
else
return false;
}
};
void test02()
{
vector<Person>v2;
Person p1("张飞", 24);
Person p2("刘备", 22);
Person p3("关羽", 25);
Person p4("孙尚香", 18);
Person p5("狄仁杰", 20);
v2.push_back(p1);
v2.push_back(p2);
v2.push_back(p3);
v2.push_back(p4);
v2.push_back(p5);
int num = count_if(v2.begin(), v2.end(),Compare2());
cout << "岁数比张飞大的人数为:" << num << endl;
}
int main()
{
test01();
test02();
return 0;
}
3.常用排序算法
sort函数
sort(iterator beg,iterator end,_Pred)
//默认排序从小到大
//_Pred谓词
void print(int val)
{
cout << val << " ";
}
void test01()
{
vector<int>v;
for (int i = 10; i>0; i--)
v.push_back(i);
sort(v.begin(), v.end());
for_each(v.begin(), v.end(), print);
cout << endl;
sort(v.begin(), v.end(), greater<int>());//逆序排列
for_each(v.begin(), v.end(), print);
}
random_shuffle函数
random_shuffle(iterator beg,iterator end)
//指定范围内的元素随机调整次序
void print(int val)
{
cout << val << " ";
}
void test01()
{
vector<int>v;
for (int i = 10; i>0; i--)
v.push_back(i);
random_shuffle(v.begin(), v.end());
for_each(v.begin(), v.end(), print);
}
为了改变随机数,可以加一个随机种子srand((unsigned)time(NULL))
merge函数
merge(iterator beg1,iterator end1,iterator beg2,iterator end2,iterator dest)
//两容器合并,并存储到另一容器中
//注意:两容器必须是有序的
//dest 目标容器开始迭代器
void print(int val)
{
cout << val << " ";
}
void test01()
{
vector<int>v1;
for (int i = 0; i<5;i++)
v1.push_back(i);
vector<int>v2;
for (int i = 5; i < 10; i++)
v2.push_back(i);
vector<int>v3;
v3.resize(10);
merge(v1.begin(), v1.end(), v2.begin(), v2.end(), v3.begin());
for_each(v3.begin(), v3.end(), print);
}
reverse函数
reverse(iterator beg,iterator end)
//反转指定容器的元素
void print(int val)
{
cout << val << " ";
}
void test01()
{
vector<int>v1;
for (int i = 0; i<5;i++)
v1.push_back(i);
reverse(v1.begin(), v1.end());
for_each(v1.begin(), v1.end(), print);
}
4.常用拷贝和替换函数
copy函数
copy(iterator beg,iterator end,iterator dest)
//将一个容器元素拷贝到另一个容器中
//dest目标开始迭代器
void print(int val)
{
cout << val << " ";
}
void test01()
{
vector<int>v1;
for (int i = 0; i<5;i++)
v1.push_back(i);
vector<int>v2;
v2.resize(5);
copy(v1.begin(), v1.end(),v2.begin());
for_each(v2.begin(), v2.end(), print);
}
replace函数
replace(iterator beg,iterator end,oldvalue,newvalue)
//oldvalue 要替换的数据
//newvalue 替换后的数据
void print(int val)
{
cout << val << " ";
}
void test01()
{
vector<int>v1;
for (int i = 0; i<5;i++)
v1.push_back(i);
replace(v1.begin(), v1.end(), 2, 2000);//将2替换成了2000
for_each(v1.begin(), v1.end(), print);
}
replace_if函数
replace_if(iterator beg,iterator end,_Pred,newvalue)
//_Pred谓词,满足条件的数据被替换成newvalue
void print(int val)
{
cout << val << " ";
}
class Compare
{
public:
bool operator()(int val)
{
return val > 3;
}
};
void test01()
{
vector<int>v1;
for (int i = 0; i<10;i++)
v1.push_back(i);
cout << "替换前:";
for_each(v1.begin(), v1.end(), print);
replace_if(v1.begin(), v1.end(), Compare(), 3000);//大于3的数据被替换成3000
cout << endl << "替换后:";
for_each(v1.begin(), v1.end(), print);
}
swap函数
swap(container c1,container c2)
//交换两个容器的元素
void print(int val)
{
cout << val << " ";
}
void test01()
{
vector<int>v1,v2;
for (int i = 0; i<10;i++)
v1.push_back(i),v2.push_back(i*2);
cout << "交换前:" << endl;
for_each(v1.begin(), v1.end(), print);
cout << endl;
for_each(v2.begin(), v2.end(), print);
swap(v1, v2);
cout << endl << "交换后:" << endl;
for_each(v1.begin(), v1.end(), print);
cout << endl;
for_each(v2.begin(), v2.end(), print);
cout << endl;
}
5.常用算术生成函数
这类算法属于小型算法,使用时要包含头文件<numeric>
accumulate函数
accumulate(iterator beg,iterator end,value)
//计算容器元素累计总和
//value 起始值
void print(int val)
{
cout << val << " ";
}
void test01()
{
vector<int>v1;
for (int i = 0; i<10;i++)
v1.push_back(i);
int total = accumulate(v1.begin(), v1.end(), 0);
cout << "total=" << total << endl;
}
fill函数
fill(iterator beg,iterator end,value)
//向容器中填充元素
//value填充的值
void print(int val)
{
cout << val << " ";
}
void test01()
{
vector<int>v1;
v1.resize(10);
//后期填充
fill(v1.begin(), v1.end(), 1000);
for_each(v1.begin(), v1.end(), print);
}
6.常用集合函数
set_intersection函数
set_intersection(iterator beg1,iterator end1,iterator beg2,iterator end2,iterator dest)
//求两个集合的交集(注意!!!这两个集合的元素必须是有序的)
//beg1 容器1开始迭代器
//end1 容器1结束迭代器
//beg2 容器2开始迭代器
//end2 容器2结束迭代器
//dest 目标容器开始迭代器
void print(int val)
{
cout << val << " ";
}
void test01()
{
vector<int>v1,v2,v3;
for (int i = 0; i < 5; i++)
v1.push_back(i);
for (int i = 0; i < 10; i++)
v2.push_back(i);
v3.resize(min(v1.size(), v2.size()));
vector<int>::iterator it = set_intersection(v1.begin(), v1.end(), v2.begin(), v2.end(), v3.begin());
for_each(v3.begin(),it, print);
}
set_union函数
set_union(iterator beg1,iterator end1,iterator beg2,iterator end2,iterator dest)
//求两个集合的并集(注意!!!两个集合必须是有序的)
//dest 目标容器开始迭代器
//目标容器开辟空间需要两个容器相加
//set_union返回值是并集中最后一个的位置
void print(int val)
{
cout << val << " ";
}
void test01()
{
vector<int>v1,v2,v3;
for (int i = 0; i < 5; i++)
v1.push_back(i);
for (int i = 0; i < 10; i++)
v2.push_back(i);
v3.resize(v1.size()+ v2.size());
vector<int>::iterator it = set_union(v1.begin(), v1.end(), v2.begin(), v2.end(), v3.begin());
for_each(v3.begin(),it, print);
}
set_difference函数
set_difference(iterator beg1,iterator end1,iterator beg2,iterator end2,iterator dest)
//求两个集合的差集(注意!!!两个集合必须是有序序列)
//dest 目标容器开始迭代器
//目标容器开辟空间需要从两个容器取最大值
//set_difference返回值既是差集中最后一个元素的位置
void print(int val)
{
cout << val << " ";
}
void test01()
{
vector<int>v1,v2,v3;
for (int i = 0; i < 10; i++)
v1.push_back(i);
for (int i = 10; i <20; i++)
v2.push_back(i);
v3.resize(max(v1.size(),v2.size()));
vector<int>::iterator it = set_difference(v1.begin(), v1.end(), v2.begin(), v2.end(), v3.begin());
cout << "v1和v2的差集:";
for_each(v3.begin(),it, print);
it = set_difference(v2.begin(), v2.end(), v1.begin(), v1.end(), v3.begin());
cout <<endl<< "v2和v1的差集:";
for_each(v3.begin(), it, print);
}