C++ STL中的unordered_map load_factor

unordered_map :: load_factor()是C++ STL中的内置函数，该函数在unordered_map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 =大小/ 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。

句法：

unordered_map_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。

示例1：

// C++ program to illustrate the
// unordered_map::load_factor() function
#include 
using namespace std;
  
int main()
{
  
    // declaration of unordered_map
    unordered_map sample;
  
    // inserts element
    sample.insert({ 1, 2 });
    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({ 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({ 11, 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: 4
The bucket_count is: 7
The load_factor is: 0.571429

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

The size is: 6
The bucket_count is: 7
The load_factor is: 0.857143

示例2：

// C++ program to illustrate the
// unordered_map::load_factor() function
#include 
using namespace std;
  
int main()
{
  
    // declaration of unordered_map
    unordered_map sample;
  
    // inserts element
    sample.insert({ 'a', 2 });
    sample.insert({ 'b', 4 });
    sample.insert({ 'c', 8 });
    sample.insert({ 'd', 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({ 'e', 0 });
    sample.insert({ 'h', 5 });
  
    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({ 'f', 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: 4
The bucket_count is: 7
The load_factor is: 0.571429

The size is: 6
The bucket_count is: 7
The load_factor is: 0.857143

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

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