C++中的std :: set_union

两个排序范围的并集
两组中的并集由一组中任一组或两个组中存在的元素形成。第二个范围中的元素在第一个范围中具有等效元素的元素不会复制到结果范围中。
在第一个版本中使用运算符<比较元素，在第二个版本中使用comp进行比较。如果(！(a 范围内的元素应已订购。
1.使用默认运算符<：

Template :
OutputIterator set_union (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.

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.

The ranges shall not overlap.

CPP

// CPP program to illustrate
// std :: set_union
#include  // std::set_union, std::sort
#include  // std::cout
#include  // std::vector
 
// Driver code
int main()
{
    int first[] = { 5, 10, 15, 20, 25 };
    int second[] = { 50, 40, 30, 20, 10 };
    int n = sizeof(first) / sizeof(first[0]);
 
    // Print first array
    std::cout << "First array contains :";
    for (int i = 0; i < n; i++)
        std::cout << " " << first[i];
    std::cout << "\n";
 
    // Print second array
    std::cout << "Second array contains :";
    for (int i = 0; i < n; i++)
        std::cout << " " << second[i];
    std::cout << "\n\n";
 
    std::vector v(10);
    std::vector::iterator it, st;
 
    std::sort(first, first + n);
    std::sort(second, second + n);
 
    // Using default function
    it = std::set_union(first, first + n, second,
                        second + n, v.begin());
 
    std::cout << "The union has " << (it - v.begin())
              << " elements:\n";
    for (st = v.begin(); st != it; ++st)
        std::cout << ' ' << *st;
    std::cout << '\n';
 
    return 0;
}

输出：

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

The union has 8 elements:
 5 10 15 20 25 30 40 50

2.使用自定义函数：
句法 ：

Template :
OutputIterator set_union (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.

The ranges shall not overlap.

CPP

// CPP program to demonstrate use of
// std :: set_symmetric_difference
#include 
#include 
#include 
#include 
 
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 subject :";
    for (int i = 0; i < n; i++)
        cout << " " << first[i];
    cout << "\n";
 
    // Print students of second list
    cout << "Students in second subject :";
    for (int i = 0; i < n; i++)
        cout << " " << second[i];
    cout << "\n\n";
 
    vector v(10);
    vector::iterator it, st;
 
    // Sorting both the list
    sort(first, first + n);
    sort(second, second + n);
 
    // Using default operator<
    it = set_union(first, first + n, second,
                          second + n, v.begin());
 
    cout << "Students attending both subjects are :\n";
    for (st = v.begin(); st != it; ++st)
        cout << ' ' << *st;
    cout << '\n';
 
    return 0;
}

输出：

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

Students attending both subjects are :
Neha Rakesh Sachin Sandeep Serena Vaibhav

可能的应用：用于查找在一个容器或两个容器中都存在的元素。
1.可以用来查找同时参加这两个科目的所有学生的名单。

CPP

// CPP program to demonstrate use of
// std :: set_symmetric_difference
#include 
#include 
#include 
#include 
 
using namespace std;
 
// Driver code
int main()
{
    string first[] = { "John", "Bob", "Mary", "Serena" };
    string second[] = { "Jim", "Mary", "John", "Bob" };
    int n = sizeof(first) / sizeof(first[0]);
 
    // Print students of first list
    cout << "Students in first subject :";
    for (int i = 0; i < n; i++)
        cout << " " << first[i];
    cout << "\n";
 
    // Print students of second list
    cout << "Students in second subject :";
    for (int i = 0; i < n; i++)
        cout << " " << second[i];
    cout << "\n\n";
 
    vector v(10);
    vector::iterator it, st;
 
    // Sorting both the list
    sort(first, first + n);
    sort(second, second + n);
 
    // Using default operator<
    it = set_union(first, first + n, second, second + n,
                   v.begin());
 
    cout << "Students attending both subjects are :\n";
    for (st = v.begin(); st != it; ++st)
        cout << ' ' << *st;
    cout << '\n';
 
    return 0;
}

输出：

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

Students attending both subjects are :
Neha Rakesh Sachin Sandeep Serena Vaibhav

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