C++ STL中的unordered_multimap equal_range()函数

unordered_multimap :: equal_range()是C++ STL中的内置函数，该函数返回所有元素的键都等于key的范围。它返回一对迭代器，其中第一个是指向范围下限的迭代器，第二个是指向范围上限的迭代器。如果容器中没有等于给定值的元素，则它将返回一对上下限都指向容器末端或unordered_multimap.end()之后的位置的对。

句法：

unordered_multimap_name.equal_range(k)

参数：该函数接受强制性参数k 。返回的范围将包含键为k的元素。

返回值：返回一对迭代器。

下面的程序说明了上述函数：

程序1：

// C++ program to illustrate the
// unordered_multimap::equal_range()
#include 
#include 
using namespace std;
  
int main()
{
  
    // declaration
    unordered_multimap sample;
  
    // inserts key and element
    sample.insert({ 1, 2 });
    sample.insert({ 1, 2 });
    sample.insert({ 2, 3 });
    sample.insert({ 3, 4 });
    sample.insert({ 2, 6 });
  
    // iterator of pairs pointing to range
    // which includes 1 and print by iterating in range
    auto itr = sample.equal_range(1);
    cout << "Elements with Key 1: ";
    for (auto it = itr.first; it != itr.second; it++) {
        cout << it->second << " ";
    }
  
    cout << endl;
  
    // iterator of pairs pointing to range
    // which includes 2 and print by iterating in range
    itr = sample.equal_range(2);
    cout << "Elements with Key 2: ";
    for (auto it = itr.first; it != itr.second; it++) {
        cout << it->second << " ";
    }
  
    return 0;
}

输出：

Elements with Key 1: 2 2 
Elements with Key 2: 6 3

程式2：

// C++ program to illustrate the
// unordered_multimap::equal_range()
#include 
#include 
using namespace std;
  
int main()
{
  
    // declaration
    unordered_multimap sample;
  
    // inserts key and element
    sample.insert({ 'a', 'b' });
    sample.insert({ 'a', 'b' });
    sample.insert({ 'a', 'd' });
    sample.insert({ 'b', 'e' });
    sample.insert({ 'b', 'd' });
  
    // iterator of pairs pointing to range
    // which includes b and print by iterating in range
    auto itr = sample.equal_range('b');
    cout << "Elements with Key b: ";
    for (auto it = itr.first; it != itr.second; it++) {
        cout << it->second << " ";
    }
  
    cout << endl;
  
    // iterator of pairs pointing to range
    // which includes a and print by iterating in range
    itr = sample.equal_range('a');
    cout << "Elements with Key a: ";
    for (auto it = itr.first; it != itr.second; it++) {
        cout << it->second << " ";
    }
  
    return 0;
}

输出：

Elements with Key b: d e 
Elements with Key a: d b b

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