C++ STL中的多集equal_range()函数

multiset :: equal_range()是C++ STL中的内置函数，它返回对的迭代器。该对是指包含容器中所有具有等于k的键的元素的范围。下界将是元素本身，上限将指向键k之后的下一个元素。如果没有与键K匹配的元素，则根据容器的内部比较对象(key_comp)，返回的范围的长度为0，两个迭代器均指向大于k的第一个元素。如果键超过set容器中的最大元素，它将返回一个迭代器，该迭代器指向过去在multiset容器中的最后一个元素。

句法：

multiset_name.equal_range(key) 

参数：该函数接受一个强制性参数键，该键指定要返回其在多集容器中的范围的键。

返回值：该函数返回一对迭代器。

下面的程序说明了上述函数。

程序1：

// CPP program to demonstrate the
// multiset::equal_range() function
#include 
using namespace std;
int main()
{
  
    multiset s;
  
    // Inserts elements
    s.insert(1);
    s.insert(6);
    s.insert(2);
    s.insert(5);
    s.insert(3);
    s.insert(3);
    s.insert(5);
    s.insert(3);
  
    // prints the multiset elements
    cout << "The multiset elements are: ";
    for (auto it = s.begin(); it != s.end(); it++)
        cout << *it << " ";
  
    // Function returns lower bound and upper bound
    auto it = s.equal_range(3);
    cout << "\nThe lower bound of 3 is " << *it.first;
    cout << "\nThe upper bound of 3 is " << *it.second;
  
    // Function returns the last element
    it = s.equal_range(10);
    cout << "\nThe lower bound of 10 is " << *it.first;
    cout << "\nThe upper bound of 10 is " << *it.second;
  
    // Function returns the range where the
    // element greater than 0 lies
    it = s.equal_range(0);
    cout << "\nThe lower bound of 0 is " << *it.first;
    cout << "\nThe upper bound of 0 is " << *it.second;
  
    return 0;
}

输出：

The multiset elements are: 1 2 3 3 3 5 5 6 
The lower bound of 3 is 3
The upper bound of 3 is 5
The lower bound of 10 is 8
The upper bound of 10 is 8
The lower bound of 0 is 1
The upper bound of 0 is 1

程式2：

// CPP program to demonstrate the
// multiset::equal_range() function
#include 
using namespace std;
int main()
{
  
    multiset s;
  
    // Inserts elements
    s.insert(1);
    s.insert(6);
    s.insert(2);
    s.insert(5);
    s.insert(3);
    s.insert(3);
    s.insert(5);
    s.insert(3);
  
    // prints the multiset elements
    cout << "The multiset elements are: ";
    for (auto it = s.begin(); it != s.end(); it++)
        cout << *it << " ";
  
    // Function returns lower bound and upper bound
    auto it = s.equal_range(3);
    cout << "\nThe lower bound of 3 is " << *it.first;
    cout << "\nThe upper bound of 3 is " << *it.second;
  
    s.erase(it.first, it.second);
  
    // prints the multiset elements after erasing the
    // range
    cout << "\nThe multiset elements are: ";
    for (auto it = s.begin(); it != s.end(); it++)
        cout << *it << " ";
  
    return 0;
}

输出：

The multiset elements are: 1 2 3 3 3 5 5 6 
The lower bound of 3 is 3
The upper bound of 3 is 5
The multiset elements are: 1 2 5 5 6

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