Zero, find
Function description:
- Find the specified element, find the iterator that returns the specified element, find the iterator that returns the end, end()
Function prototype:
-
find(iterator beg, iterator end, value);// Find the element by value, find the iterator to return to the specified position, find the iterator to return to the end position
// beg starts iterator
// end ends the iterator
// value to find the element
Example:
#include <algorithm>
#include <vector>
#include <string>
void test01() {
vector<int> v;
for (int i = 0; i < 10; i++) {
v.push_back(i + 1);
}
//查找容器中是否有 5 这个元素
vector<int>::iterator it = find(v.begin(), v.end(), 5);
if (it == v.end())
{
cout << "没有找到!" << endl;
}
else
{
cout << "找到:" << *it << endl;
}
}
class Person {
public:
Person(string name, int age)
{
this->m_Name = name;
this->m_Age = age;
}
//重载==
bool operator==(const Person& p)
{
if (this->m_Name == p.m_Name && this->m_Age == p.m_Age)
{
return true;
}
return false;
}
public:
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);
v.push_back(p1);
v.push_back(p2);
v.push_back(p3);
v.push_back(p4);
vector<Person>::iterator it = find(v.begin(), v.end(), p2);
if (it == v.end())
{
cout << "没有找到!" << endl;
}
else
{
cout << "找到姓名:" << it->m_Name << " 年龄: " << it->m_Age << endl;
}
}
to sum up:
To find a custom type with find, be sure to overload the == operator.
Use find to find the specified element in the container, and the return value is an iterator.
一、find_if
Function description:
- Find elements by condition
Function prototype:
-
find_if(iterator beg, iterator end, _Pred);// Find the element by value, find the iterator to return to the specified position, find the iterator to return to the end position
// beg starts iterator
// end ends the iterator
// _Pred function or predicate (return bool type functor)
Example:
#include <algorithm>
#include <vector>
#include <string>
//内置数据类型
class GreaterFive
{
public:
bool operator()(int val)
{
return val > 5;
}
};
void test01() {
vector<int> v;
for (int i = 0; i < 10; i++) {
v.push_back(i + 1);
}
vector<int>::iterator it = find_if(v.begin(), v.end(), GreaterFive());
if (it == v.end()) {
cout << "没有找到!" << endl;
}
else {
cout << "找到大于5的数字:" << *it << endl;
}
}
//自定义数据类型
class Person {
public:
Person(string name, int age)
{
this->m_Name = name;
this->m_Age = age;
}
public:
string m_Name;
int m_Age;
};
class Greater20
{
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);
v.push_back(p1);
v.push_back(p2);
v.push_back(p3);
v.push_back(p4);
vector<Person>::iterator it = find_if(v.begin(), v.end(), Greater20());
if (it == v.end())
{
cout << "没有找到!" << endl;
}
else
{
cout << "找到姓名:" << it->m_Name << " 年龄: " << it->m_Age << endl;
}
}
int main() {
//test01();
test02();
system("pause");
return 0;
}
Summary: find_if search by condition makes the search more flexible, and the provided functor can change different strategies
Two, adjacent_find
Function description:
- Find adjacent duplicate elements
Function prototype:
-
adjacent_find(iterator beg, iterator end);// Find adjacent repeated elements and return an iterator to the first position of adjacent elements
// beg starts iterator
// end ends the iterator
Example:
#include <algorithm>
#include <vector>
void test01()
{
vector<int> v;
v.push_back(1);
v.push_back(2);
v.push_back(5);
v.push_back(2);
v.push_back(4);
v.push_back(4);
v.push_back(3);
//查找相邻重复元素
vector<int>::iterator it = adjacent_find(v.begin(), v.end());
if (it == v.end()) {
cout << "找不到!" << endl;
}
else {
cout << "找到相邻重复元素为:" << *it << endl;
}
}
三、binary_search
Function description:
- Find if the specified element exists
Function prototype:
-
bool binary_search(iterator beg, iterator end, value);// Find the specified element, return true if found, otherwise false
// Note: Not available in unordered sequence
// beg starts iterator
// end ends the iterator
// value to find the element
Example:
#include <algorithm>
#include <vector>
void test01()
{
vector<int>v;
for (int i = 0; i < 10; i++)
{
v.push_back(i);
}
//二分查找
bool ret = binary_search(v.begin(), v.end(),2);
if (ret)
{
cout << "找到了" << endl;
}
else
{
cout << "未找到" << endl;
}
}
int main() {
test01();
system("pause");
return 0;
}
**Summary:** The binary search method is very efficient. It is worth noting that the ordered sequence of the elements in the search container must be
Four, count
Function description:
- Count the number of elements
Function prototype:
-
count(iterator beg, iterator end, value);// Count the number of occurrences of elements
// beg starts iterator
// end ends the iterator
// value statistic element
Example:
#include <algorithm>
#include <vector>
//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(v.begin(), v.end(), 4);
cout << "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;
}
bool operator==(const Person & p)
{
if (this->m_Age == p.m_Age)
{
return true;
}
else
{
return false;
}
}
string m_Name;
int m_Age;
};
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", 25);
v.push_back(p1);
v.push_back(p2);
v.push_back(p3);
v.push_back(p4);
v.push_back(p5);
Person p("诸葛亮",35);
int num = count(v.begin(), v.end(), p);
cout << "num = " << num << endl;
}
int main() {
//test01();
test02();
system("pause");
return 0;
}
Summary: When counting custom data types, you need to cooperate with overloading operator==
五、count_if
Function description:
- Count the number of elements according to conditions
Function prototype:
-
count_if(iterator beg, iterator end, _Pred);// Count the number of occurrences of elements according to conditions
// beg starts iterator
// end ends the iterator
// _Pred predicate
Example:
#include <algorithm>
#include <vector>
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", 25);
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();
system("pause");
return 0;
}
**Summary: **Use count for statistics by value, count_if for statistics by conditions