C++ unordered_multimap::bucket_size() 函数

C++ 的std::unordered_multimap::bucket_size() 函数用于返回第 n 个桶中存在的元素数量。桶是容器内部哈希表中的一个槽，元素根据其键的哈希值分配到该槽中。其范围从 0 到 bucket_count - 1。

语法

以下是 std::unordered_multimap::bucket_size() 的语法。

size_type bucket_size(size_type n) const;

参数

• n - 它表示桶号，应小于 bucket_count。

返回值

此函数返回当前桶中的元素总数。

示例 1

在以下示例中，让我们看看 unordered_multimap::bucket_size() 函数的用法。

#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;
}

输出

如果我们运行以上代码，它将生成以下输出：

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

考虑以下示例，我们将使用 bucket_size() 函数获取每个桶中存在的元素计数。

#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;
}

输出

以下是以上代码的输出：

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

让我们看看以下示例，我们将使用 bucket_size() 函数。

#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;
}

输出

以上代码的输出如下：

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.