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Common search algorithms

【 Introduction 】 :

find; // Find elements
find_if; // Find elements by condition
adjacent_find; // Find adjacent repeating elements
binary_search; // Binary search
count; // Count elements
count_if; // Count elements by conditions

find

【 Function 】 :

The iterator that returns the specified element is not found. End ()Copy the code

Function prototype:

find(iterator begin,iterator end,value);

// begin begins the iterator // end ends the iterator // value the element to be searchedCopy the code

“Demo” :

#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
using namespace std;

class Person
{
public:
    Person(string name, int age)
    {
        this->m_Name = name;
        this->m_Age = age;
    }
    
    / / overloaded = =
    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 test01(a)
{
    vector<int> v;
    for (int i = 0; i < 10; i++)
    {
        v.push_back(i);
    }

    // Find if there is 5 in the container
    vector<int>::iterator it = find(v.begin(), v.end(), 5);
    if(it ! = v.end())
    {
        cout << "Found it." << *it << endl;
    }
    else
    {
        cout << "Not found"<< endl; }}void test02(a)
{
    vector<Person> v;
    Person p1("Zhang".20);
    Person p2("Bill".19);
    Person p3("Fifty".21);
    Person p4("Daisy".22);
    v.push_back(p1);
    v.push_back(p2);
    v.push_back(p3);
    v.push_back(p4);
    
    Person targetP("Fifty".21);
    vector<Person>::iterator it = find(v.begin(), v.end(), targetP);
    if(it ! = v.end())
    {
        cout << "Found it." << it->m_Name << "," << it->m_Age << endl;
    }
    else
    {
        cout << "Not found"<< endl; }}int main(a)
{
    test01(a);test02(a);return 0;
}
Copy the code

Summary: We use find to find the specified element in a container, and the return value is an iterator

find_if

【 Function 】 :

Find elements by conditionCopy the code

Function prototype:

find_if(iterator begin,iterator end,_Pred);

// begin begins iterator // end ends iterator // _Pred function or predicate (return bool functor)Copy the code

“Demo” :

#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

// Built-in data types
class GreaterFive
{
public:
    bool operator(a)(int v)
    {
        return v > 5; }};void test01(a)
{
    vector<int> v;
    for (int i = 0; i < 10; i++)
    {
        v.push_back(i);
    }

    vector<int>::iterator it = find_if(v.begin(), v.end(), GreaterFive());
    if(it ! = v.end())
    {
        cout << "Look for numbers greater than 5:" << *it << endl;
    }
    else
    {
        cout << "Not found"<< endl; }}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(a)(Person &p)
    {
        return p.m_Age > 20; }};void test02(a)
{

    Person p1("Zhang".20);
    Person p2("Bill".22);
    Person p3("Fifty".19);
    vector<Person> v;
    v.push_back(p1);
    v.push_back(p2);
    v.push_back(p3);

    vector<Person>::iterator it = find_if(v.begin(), v.end(), Greater20());
    if(it ! = v.end())
    {
        cout << "Looking for someone over 20:" << it->m_Name << "," << it->m_Age << endl;
    }
    else
    {
        cout << "Not found"<< endl; }}int main(a)
{
    test01(a);test02(a);return 0;
}
Copy the code

Summary: Find_if conditional lookup is more flexible and provides a function that can change different strategies

adjacent_find

【 Function 】 :

Find adjacent repeating elementsCopy the code

Function prototype:

adjacent_find(iterator begin,iterator end);

// Find adjacent repeating elements, return the iterator at the first position of adjacent elements // begin start iterator // end end iteratorCopy the code

“Demo” :

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;
void test01(a)
{
    vector<int> v;
    v.push_back(0);
    v.push_back(1);
    v.push_back(2);
    v.push_back(2);
    v.push_back(3);
    v.push_back(3);

    // Find adjacent repeating elements
    vector<int>::iterator it = adjacent_find(v.begin(), v.end());
    if(it ! = v.end())
    {
        cout << "Duplicate elements found:" << *it << endl;
    }
    else
    {
        cout << "Duplicate element not found"<< endl; }}int main(a)
{
    test01(a);return 0;
}
Copy the code

Summary: Use the adjacent_find algorithm in THE STL to find adjacent repeating elements in an interview question

binary_search

【 Function 】 :

Finds whether the specified element existsCopy the code

Function prototype:

bool binary_search(iterator begin,iterator end,value);

// Find the specified element, return true, otherwise return false; // Note: ** cannot be used in ** unordered sequences ** // begin begins the iterator // end ends the iterator // value looks for the elementCopy the code

“Demo” :

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;
void test01(a)
{

    vector<int> v;
    for (int i = 0; i < 10; i++)
    {
        v.push_back(i);
    }

    // Binary search
    bool ret = binary_search(v.begin(), v.end(), 2);
    if (ret)
    {
        cout << "Found it." << endl;
    }
    else
    {
        cout << "Not found"<< endl; }}int main(a)
{
    test01(a);return 0;
}
Copy the code

Summary: Binary lookup is efficient, but the elements in the lookup container must be ordered

count

【 Function 】 :

Number of statistical elementsCopy the code

Function prototype:

count(iterator begin,iterator end,value);

// Count the number of occurrences of an element // begin Start iterator // end End iterator // value Count the elementCopy the code

“Demo” :

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

// Customize the data type
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;
        }
        return false;
    }

public:
    string m_Name;
    int m_Age;
};

void test01(a)
{
    vector<int> v;
    v.push_back(0);
    v.push_back(0);
    v.push_back(1);
    v.push_back(2);
    v.push_back(2);
    v.push_back(3);

    int num = count(v.begin(), v.end(), 2);
    cout << "2 appears :" << num << "Time" << endl;
}

void test02(a)
{
    Person p1("Zhang".20);
    Person p2("Bill".20);
    Person p3("Fifty".20);
    vector<Person> v;
    v.push_back(p1);
    v.push_back(p2);
    v.push_back(p3);

    Person pTarget("Xiao Ming".20);
    int num = count(v.begin(), v.end(), pTarget);
    cout << "20-year-olds have it." << num << "People" << endl;
}

int main(a)
{
    test01(a);test02(a);return 0;
}
Copy the code

Note: When the statistics are of a customized data type, overloaded operator== is required

count_if

【 Function 】 :

Count the number of elements by conditionCopy the code

Function prototype:

count_if(iterator begin,iterator end,_Pred);

// start iterator // end iterator // _Pred predicateCopy the code

“Demo” :

#include <iostream>
#include <algorithm>
#include <vector>
#include <string>

using namespace std;

class GreaterFive
{
public:
    bool operator(a)(int v)
    {
        return v > 5; }};// Customize the data type
class Person
{
public:
    Person(string name, int age)
    {
        this->m_Name = name;
        this->m_Age = age;
    }

public:
    string m_Name;
    int m_Age;
};
class AgeGreater20
{
public:
    bool operator(a)(Person &p)
    {
        return p.m_Age > 20; }};void test01(a)
{
    vector<int> v;
    for (int i = 0; i < 10; i++)
    {
        v.push_back(i);
    }

    int num = count_if(v.begin(), v.end(), GreaterFive());
    cout << "The numbers greater than 5 are << num << "个" << endl;
}

void test02(a)
{
    Person p1("Zhang".20);
    Person p2("Bill".21);
    Person p3("Fifty".22);
    Person p4("Daisy".23);

    vector<Person> v;
    v.push_back(p1);
    v.push_back(p2);
    v.push_back(p3);
    v.push_back(p4);

    int num = count_if(v.begin(), v.end(), AgeGreater20());
    cout << "Those over the age of 20 << num << "People" << endl;
}
int main(a)
{
    test01(a);test02(a);return 0;
}
Copy the code

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【c++ common search algorithm 】

Common search algorithms

find

find_if

adjacent_find

binary_search

count

count_if

【c++ common search algorithm 】

Common search algorithms

find

find_if

adjacent_find

binary_search

count

count_if

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