C++ unordered_map load_factor用法及代码示例

unordered_map::load_factor()是C++ STL中的内置函数，该函数返回unordered_map容器中的当前负载系数。负载系数是容器中的元素数量(size)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_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 <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
  
    // declaration of unordered_map 
    unordered_map<int, int> 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 <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
  
    // declaration of unordered_map 
    unordered_map<char, int> 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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注：本文由纯净天空筛选整理自ankit15697大神的英文原创作品 unordered_map load_factor 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。