C++ unordered_multimap::bucket_size() 函式

C++ 的std::unordered_multimap::bucket_size() 函式用於返回第 n 個桶中存在的元素數量。桶是容器內部雜湊表中的一個槽，元素根據其鍵的雜湊值分配到該槽中。其範圍從 0 到 bucket_count - 1。

語法

以下是 std::unordered_multimap::bucket_size() 的語法。

size_type bucket_size(size_type n) const;

引數

• n - 它表示桶號，應小於 bucket_count。

返回值

此函式返回當前桶中的元素總數。

示例 1

在以下示例中，讓我們看看 unordered_multimap::bucket_size() 函式的用法。

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void) {
   unordered_multimap<char, int> umm = {
      {'a', 1},
      {'b', 2},
      {'c', 3},
      {'d', 4},
      {'e', 5}
   };
   for (int i = 0; i < umm.bucket_count(); ++i)
      cout << "Bucket " << i << " contains "<< umm.bucket_size(i) << " elements." << endl;
   return 0;
}

輸出

如果我們執行以上程式碼，它將生成以下輸出：

Bucket 0 contains 2 elements.
Bucket 1 contains 2 elements.
Bucket 2 contains 0 elements.
Bucket 3 contains 0 elements.
Bucket 4 contains 0 elements.
Bucket 5 contains 0 elements.
Bucket 6 contains 2 elements.

示例 2

考慮以下示例，我們將使用 bucket_size() 函式獲取每個桶中存在的元素計數。

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void) {
   unordered_multimap<char, int> umm;
   umm.insert({ {'a', 10}, {'b', 20}, {'a', 10}, {'b', 30}, {'c', 40} });
   
   for (int i = 0; i < umm.bucket_count(); ++i)
      cout << "Bucket " << i << " contains "<< umm.bucket_size(i) << " elements." << endl;
   return 0;
}

輸出

以下是以上程式碼的輸出：

Bucket 0 contains 0 elements.
Bucket 1 contains 0 elements.
Bucket 2 contains 0 elements.
Bucket 3 contains 0 elements.
Bucket 4 contains 0 elements.
Bucket 5 contains 0 elements.
Bucket 6 contains 2 elements.
Bucket 7 contains 2 elements.
Bucket 8 contains 1 elements.
Bucket 9 contains 0 elements.
Bucket 10 contains 0 elements.
Bucket 11 contains 0 elements.
Bucket 12 contains 0 elements.

示例 3

讓我們看看以下示例，我們將使用 bucket_size() 函式。

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void) {
   unordered_multimap<char, int> umm;
   umm.insert({ {'a', 10}, {'b', 20}, {'a', 10}, {'b', 30}, {'c', 40} });
   for (int i = 0; i < umm.bucket_count(); ++i){
      if(i%2!=0){
         cout << "Bucket " << i << " contains "<< umm.bucket_size(i) << " elements." << endl;
      }
   }
   return 0;
}

輸出

以上程式碼的輸出如下：

Bucket 1 contains 0 elements.
Bucket 3 contains 0 elements.
Bucket 5 contains 0 elements.
Bucket 7 contains 2 elements.
Bucket 9 contains 0 elements.
Bucket 11 contains 0 elements.