C++ STL中的unordered_multimap load_factor()函数

unordered_multimap :: load_factor()是C++ STL中的内置函数，该函数返回在unordered_multimap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_multimap_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_multimap :: load_factor()函数：

程序1 ：

// C++ program to illustrate the
// unordered_multimap::load_factor() function
#include 
#include 
using namespace std;
  
int main()
{
  
    // declaration
    unordered_multimap sample;
  
    // inserts element
    sample.insert({ 1, 2 });
    sample.insert({ 1, 3 });
    sample.insert({ 2, 4 });
    sample.insert({ 5, 8 });
    sample.insert({ 7, 10 });
  
    cout << "The size is: " << sample.size();
    cout << "\nThe bucket_count is: "
         << sample.bucket_count();
  
    cout << "\nThe load_factor is: "
         << sample.load_factor();
  
    sample.insert({ 1, 1 });
    sample.insert({ 9, 0 });
  
    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({ 1, 1 });
  
    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_multimap::load_factor()
#include 
#include 
using namespace std;
  
int main()
{
  
    // declaration
    unordered_multimap sample;
  
    // inserts element
    sample.insert({ 'a', 'b' });
    sample.insert({ 'a', 'b' });
    sample.insert({ 'a', 'd' });
    sample.insert({ 'b', 'e' });
    sample.insert({ 'b', '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({ 'b', 'k' });
    sample.insert({ 'b', 'h' });
  
    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', 'j' });
  
    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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