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C++ 算法中的 set_union函数

C++算法 set_union()函数用于查找两个排序参数[first1，last1)和[first2，last2)的并集，这两个元素由任一集合中的元素形成或两者兼而有之。

set_union - 语法

default (1)     template <class InputIterator1, class InputIterator2, class OutputIterator>
                        OutputIterator set_union (InputIterator1 first1, InputIterator1 last1,
                            InputIterator2 first2, InputIterator2 last2, OutputIterator result);

custom (2)     template <class InputIterator1, class InputIterator2,
                     class OutputIterator, class Compare>
                   OutputIterator set_union (InputIterator1 first1, InputIterator1 last1,
              InputIterator2 first2, InputIterator2 last2, OutputIterator result, Compare comp);

set_union - 参数

first1 :一个输入迭代器，它指向两个已排序源序列中第一个的第一个元素。

last1 :一个输入迭代器，它指向两个已排序源序列中第一个序列中的最后一个元素。

first2 :一个输入迭代器，它指向第二个排序的源序列中的第一个元素。

last2 :一个输入迭代器，指向第二个排序的源序列中的最后一个元素。

comp :用户定义的二进制谓词函数，该函数接受两个参数，如果两个参数顺序正确，则返回true，否则返回false。

result:一个输出迭代器，它指向目标参数中第一个元素的位置。

set_union - 返回值

此函数将迭代器返回到构造参数的末尾。

set_union - 例子1

让我们看一个简单的示例来演示set_union()的用法:

链接：https://www.learnfk.comhttps://www.learnfk.com/c++/cpp-algorithm-set-union-function.html

来源：LearnFk无涯教程网

在线运行复制代码

#include <iostream>
#include <set>
#include <list>
#include <vector>
#include <algorithm>
#include <iterator>

using namespace std;

int main()
{
  list<int> a = {1, 2, 3, 4};
  multiset<int> b = {4, 5, 6, 2};
  vector<int> result;

  set_union(begin(a), end(a),
                 begin(b), end(b),
                 inserter(result, end(result)));

  for_each(begin(result), end(result), [](int x) {
    cout << x << endl;
  });
  
  return 0;
}

输出:

set_union - 例子2

让我们看另一个简单的例子:

在线运行复制代码

#include <iostream>    //std::cout
#include <algorithm>   //std::set_union, std::sort
#include <vector>      //std::vector

using namespace std;

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 
    cout << "First array contains:"; 
    for (int i = 0; i < n; i++) 
        cout << " " << first[i]; 
    cout << "\n"; 
  
   //Print second array 
    cout << "Second array contains:"; 
    for (int i = 0; i < n; i++) 
        cout << " " << second[i]; 
    cout << "\n\n"; 
  
    vector<int> v(10); 
    vector<int>::iterator it, st; 
  
    sort(first, first + n); 
    sort(second, second + n); 
  
   //Using default function 
    it = set_union(first, first + n, second, second + n, v.begin()); 
  
    cout << "The union has " << (it - v.begin()) << " elements:\n"; 
    for (st = v.begin(); st != it; ++st) 
        cout << ' ' << *st; 
    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

set_union - 例子3

让我们看另一个简单的示例，查找同时参加这两个科目的所有学生的列表:

在线运行复制代码

#include <iostream> 
#include <algorithm> 
#include <vector> 
#include <string> 
  
using namespace std; 
  
// Driver code 
int main() 
{ 
    string first[] = { "Nikita", "Divya", "Deep", "Kashish" }; 
    string second[] = { "Aman", "Nikita", "Amita", "Deep" }; 
    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<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_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: Nikita Divya Deep Kashish
Students in second subject: Aman Nikita Amita Deep

Students attending both subjects are:
 Aman Amita Deep Divya Kashish Nikita

set_union - 例子4

让我们看一个简单的例子:

在线运行复制代码

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

using namespace std;
 
int main()
{ 
    vector<char> v1 = {'A', 'B', 'C'}; 
    vector<char> v2 = {      'C', 'D', 'E', 'F'}; 
    
    vector<char> dest1;
 
    set_union(v1.begin(), v1.end(),
                   v2.begin(), v2.end(),                  
                   back_inserter(dest1));
 
    for (const auto &i : dest1) {
        cout << i << ' ';
    }   
    cout << '\n';
    
    return 0;
}