C++ unordered_multimap equal_range()用法及代码示例

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键的范围。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或unordered_multimap.end()末尾的位置。

用法:

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：它返回一对迭代器。

以下示例程序旨在说明上述函数：

示例1:

// C++ program to illustrate the 
// unordered_multimap::equal_range() 
#include <iostream> 
#include <unordered_map> 
using namespace std; 
  
int main() 
{ 
  
    // declaration 
    unordered_multimap<int, int> 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

示例2:

// C++ program to illustrate the 
// unordered_multimap::equal_range() 
#include <iostream> 
#include <unordered_map> 
using namespace std; 
  
int main() 
{ 
  
    // declaration 
    unordered_multimap<char, char> 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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注：本文由纯净天空筛选整理自gopaldave大神的英文原创作品 unordered_multimap equal_range() function in C++ STL。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。