C++ unordered_set load_factor()用法及代码示例

unordered_set::load_factor()是C++ STL中的内置函数，该函数返回unordered_set容器中的当前负载系数。负载系数是容器中的元素数量(其大小)与铲斗数量(bucket_count)之比：

load_factor = size / bucket_count

负载因子会影响哈希表中发生冲突的概率(即，两个元素位于同一存储桶中的概率)。通过在每次需要扩展时进行重新哈希处理，容器会自动增加铲斗数，以将负载系数保持在特定阈值以下(其max_load_factor)。

用法：

unordered_set_name.load_factor()

参数：该函数不接受任何参数。

返回值：该函数返回当前的负载系数。它可以是整数或双精度类型。

以下示例程序旨在说明unordered_set::load_factor()函数：

示例1:：

// C++ program to illustrate the 
// unordered_set::load_factor() function 
#include <iostream> 
#include <unordered_set> 
using namespace std; 
  
int main() 
{ 
  
    // declaration 
    unordered_set<int> sample; 
  
    // inserts element 
    sample.insert(1); 
    sample.insert(11); 
    sample.insert(111); 
    sample.insert(12); 
    sample.insert(13); 
  
    cout << "The size is: " << sample.size(); 
    cout << "\nThe bucket_count is: "
         << sample.bucket_count(); 
  
    cout << "\nThe load_factor is: "
         << sample.load_factor(); 
  
    sample.insert(2); 
    sample.insert(22); 
  
    cout << "\n\nThe size is: "
         << sample.size(); 
  
    cout << "\nThe bucket_count is: "
         << sample.bucket_count(); 
  
    cout << "\nThe load_factor is: "
         << sample.load_factor(); 
  
    sample.insert(33); 
  
    cout << "\n\nThe size is: "
         << sample.size(); 
  
    cout << "\nThe bucket_count is: "
         << sample.bucket_count(); 
  
    cout << "\nThe load_factor is: "
         << sample.load_factor(); 
    return 0; 
}

输出：

The size is: 5
The bucket_count is: 7
The load_factor is: 0.714286

The size is: 7
The bucket_count is: 17
The load_factor is: 0.411765

The size is: 8
The bucket_count is: 17
The load_factor is: 0.470588

示例2:：

// C++ program to illustrate the 
// unordered_set::load_factor() function 
#include <iostream> 
#include <unordered_set> 
using namespace std; 
  
int main() 
{ 
  
    // declaration 
    unordered_set<char> sample; 
  
    // inserts element 
    sample.insert('a'); 
    sample.insert('b'); 
    sample.insert('c'); 
    sample.insert('r'); 
    sample.insert('d'); 
  
    cout << "The size is: " << sample.size(); 
    cout << "\nThe bucket_count is: "
         << sample.bucket_count(); 
  
    cout << "\nThe load_factor is: "
         << sample.load_factor(); 
  
    sample.insert('f'); 
    sample.insert('k'); 
  
    cout << "\n\nThe size is: "
         << sample.size(); 
  
    cout << "\nThe bucket_count is: "
         << sample.bucket_count(); 
  
    cout << "\nThe load_factor is: "
         << sample.load_factor(); 
  
    sample.insert('z'); 
  
    cout << "\n\nThe size is: "
         << sample.size(); 
  
    cout << "\nThe bucket_count is: "
         << sample.bucket_count(); 
  
    cout << "\nThe load_factor is: "
         << sample.load_factor(); 
    return 0; 
}

输出：

The size is: 5
The bucket_count is: 7
The load_factor is: 0.714286

The size is: 7
The bucket_count is: 17
The load_factor is: 0.411765

The size is: 8
The bucket_count is: 17
The load_factor is: 0.470588

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注：本文由纯净天空筛选整理自Aman Goyal 2大神的英文原创作品 unordered_set load_factor() 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。