C++ unordered_map load_factor用法及代碼示例

unordered_map::load_factor()是C++ STL中的內置函數，該函數返回unordered_map容器中的當前負載係數。負載係數是容器中的元素數量(size)與鏟鬥數量(bucket_count)之比：
load_factor =size/bucket_count
負載因子會影響哈希表中發生衝突的概率(即，兩個元素位於同一存儲桶中的概率)。通過在每次需要擴展時進行重新哈希處理，容器會自動增加鏟鬥數，以將負載係數保持在特定閾值以下(其max_load_factor)。

用法:

unordered_map_name.load_factor()

參數：該函數不接受任何參數。

返回值：該函數返回當前的負載係數。

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; 
}

輸出：

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; 
}

輸出：

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：本文由純淨天空篩選整理自ankit15697大神的英文原創作品 unordered_map load_factor in C++ STL。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。