C++ STL中的unordered_set load_factor()函数

unordered_set :: load_factor()是C++ STL中的内置函数，该函数在unordered_set容器中返回当前的加载因子。负载因子是容器中元素数量(其大小)与存储桶数量(bucket_count)之间的比率：

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一次重新哈希处理，容器会自动增加存储桶的数量，以将负载系数保持在特定阈值(其max_load_factor)以下。

语法：

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。

下面的程序说明了unordered_set :: load_factor()函数：

程序1 ：

// C++ program to illustrate the
// unordered_set::load_factor() function
#include 
#include 
using namespace std;
  
int main()
{
  
    // declaration
    unordered_set 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

程序2 ：

// C++ program to illustrate the
// unordered_set::load_factor() function
#include 
#include 
using namespace std;
  
int main()
{
  
    // declaration
    unordered_set 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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