std::set_difference en C++

La diferencia de dos conjuntos está formada por los elementos que están presentes en el primer conjunto, pero no en el segundo. Los elementos copiados por la función vienen siempre del primer rango, en el mismo orden. Los elementos de ambas gamas ya deben estar ordenados. 

1. Comparación de elementos usando “<“: 

Sintaxis:

Template :
OutputIterator set_difference (InputIterator1 first1, InputIterator1 last1,
                               InputIterator2 first2, InputIterator2 last2,
                               OutputIterator result);

Parameters :

first1, last1
Input iterators to the initial and final positions of the first
sorted sequence. The range used is [first1, last1), which contains
all the elements between first1 and last1, including the element
pointed by first1 but not the element pointed by last1.
first2, last2
Input iterators to the initial and final positions of the second
sorted sequence. The range used is [first2, last2).

result
Output iterator to the initial position of the range where the
resulting sequence is stored.
The pointed type shall support being assigned the value of an
element from the first range.

Return Type :
An iterator to the end of the constructed range.

// CPP program to illustrate
// std :: set_difference
 
#include <bits/stdc++.h>
 
int main()
{
    int first[] = { 5, 10, 15, 20, 25 };
    int second[] = { 50, 40, 30, 20, 10 };
    int n = sizeof(first) / sizeof(first[0]);
 
    std::vector<int> v2(5);
    std::vector<int>::iterator it, ls;
 
    std::sort(first, first + 5);
    std::sort(second, second + 5);
 
    // Print elements
    std::cout << "First array :";
    for (int i = 0; i < n; i++)
        std::cout << " " << first[i];
    std::cout << "\n";
 
    // Print elements
    std::cout << "Second array :";
    for (int i = 0; i < n; i++)
        std::cout << " " << second[i];
    std::cout << "\n\n";
 
    // using default comparison
    /* first array intersection second array */
    ls = std::set_difference(first, first + 5, second, second + 5, v2.begin());
 
    std::cout << "Using default comparison, \n";
    std::cout << "The difference has " << (ls - v2.begin()) << " elements :";
    for (it = v2.begin(); it < ls; ++it)
        std::cout << " " << *it;
    std::cout << "\n";
 
    return 0;
}

Producción:

First array : 5 10 15 20 25
Second array : 10 20 30 40 50

Using default comparison,
The difference has 3 elements : 5 15 25

2. Al comparar usando una función predefinida:

Template :
OutputIterator set_difference (InputIterator1 first1, InputIterator1 last1,
                               InputIterator2 first2, InputIterator2 last2,
                               OutputIterator result, Compare comp);

Parameters :

first1, last1, first2, last2, result are same as above.

comp
Binary function that accepts two arguments of the types pointed
by the input iterators, and returns a value convertible to bool.
The function shall not modify any of its arguments.
This can either be a function pointer or a function object.

Return Type :
An iterator to the end of the constructed range.

// CPP program to illustrate
// std :: set_difference
 
#include <bits/stdc++.h>
 
bool comp(int i, int j)
{
    return (i < j);
}
 
int main()
{
    int first[] = { 50, 40, 30, 20, 10 };
    int second[] = { 5, 10, 15, 20, 25 };
    int n = sizeof(first) / sizeof(first[0]);
 
    std::vector<int> v1(5);
 
    std::sort(first, first + 5);
    std::sort(second, second + 5);
 
    // Print elements
    std::cout << "First array :";
    for (int i = 0; i < n; i++)
        std::cout << " " << first[i];
    std::cout << "\n";
 
    // Print elements
    std::cout << "Second array :";
    for (int i = 0; i < n; i++)
        std::cout << " " << second[i];
    std::cout << "\n\n";
 
    // using custom comparison, function as comp
    /* first array intersection second array */
    ls = std::set_difference(second, second + 5, first, first + 5, v1.begin(), comp);
 
    std::cout << "Using custom comparison, \n";
    std::cout << "The difference has " << (ls - v1.begin()) << " elements :";
    for (it = v1.begin(); it < ls; ++it)
        std::cout << " " << *it;
    std::cout << "\n";
 
    return 0;
}

Producción:

First array : 10 20 30 40 50
Second array : 5 10 15 20 25

Using custom comparison :
The difference has 3 elements : 30 40 50

Posible aplicación: se utiliza para encontrar los elementos que están presentes solo en la primera lista y no en la segunda lista. 1. Se puede usar para encontrar la lista de estudiantes que asisten solo a las primeras clases. 

// CPP program to demonstrate use of
// std :: set_difference
#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
 
using namespace std;
 
// Driver code
int main()
{
    string first[] = { "Sachin", "Rakesh", "Sandeep", "Serena" };
    string second[] = { "Vaibhav", "Sandeep", "Rakesh", "Neha" };
    int n = sizeof(first) / sizeof(first[0]);
 
    // Print students of first list
    cout << "Students in first class :";
    for (int i = 0; i < n; i++)
        cout << " " << first[i];
    cout << "\n";
 
    // Print students of second list
    cout << "Students in second class :";
    for (int i = 0; i < n; i++)
        cout << " " << second[i];
    cout << "\n\n";
 
    vector<string> v(10);
    vector<string>::iterator it, st;
 
    // Sorting both the list
    sort(first, first + n);
    sort(second, second + n);
 
    // Using default operator<
    it = set_difference(first, first + n, second, second + n, v.begin());
 
    cout << "Students attending first class only are :\n";
    for (st = v.begin(); st != it; ++st)
        cout << ' ' << *st;
    cout << '\n';
 
    return 0;
}

PRODUCCIÓN :

Students in first class : Sachin Rakesh Sandeep Serena
Students in second class : Vaibhav Sandeep Rakesh Neha

Students attending first classes only are :
 Sachin Serena

2. También se puede usar para encontrar los elementos que no están presentes en la primera lista solamente. El programa se da arriba. Este artículo es una contribución de Sachin Bisht . Si te gusta GeeksforGeeks y te gustaría contribuir, también puedes escribir un artículo usando write.geeksforgeeks.org o enviar tu artículo por correo a review-team@geeksforgeeks.org. Vea su artículo que aparece en la página principal de GeeksforGeeks y ayude a otros Geeks. Escriba comentarios si encuentra algo incorrecto o si desea compartir más información sobre el tema tratado anteriormente.