C++ unordered_map::bucket_size() 函数



C++ 函数unordered_map::bucket_size() 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。桶的编号范围从 0 到 (bucket_count - 1)。

此函数返回每个桶中的元素数量,该数量始终小于总数。

语法

以下是 unordered_map::bucket_size() 函数的语法。

unordered_map.bucket_size(n);

参数

  • n - 指示桶号,它是一个无符号整数,应小于 bucket_count。

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返回值

返回一个无符号整数,表示当前桶中元素的总数。

示例 1

以下示例将使用 unordered_map::bucket_size()。

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

输出

以上代码的输出如下:

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 1 elements.
Bucket 7 contains 1 elements.
Bucket 8 contains 1 elements.
Bucket 9 contains 1 elements.
Bucket 10 contains 1 elements.
Bucket 11 contains 0 elements.
Bucket 12 contains 0 elements.

示例 2

考虑以下示例,我们将计算桶的数量。

Open Compiler
#include <iostream> #include <string> #include <unordered_map> using namespace std; int main () { std::unordered_map<std::string,std::string> map = { {"us","United States"}, {"uk","United Kingdom"}, {"fr","France"}, }; unsigned totalbuckets = map.bucket_count(); unsigned element = map.bucket_size(9); cout<<"total number of buckets"<<": "<<totalbuckets<<endl; cout << "bucket 9 has " << element << " element:\n"; return 0; }

输出

以上代码的输出如下:

total number of buckets: 13
bucket 9 has 1 element:

示例

在以下示例中,我们获取当前 unordered_map 中至少包含一个元素的桶的数量及其元素大小。

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

输出

让我们编译并运行以上程序,这将产生以下结果:

Bucket 6 contains 1 elements.
Bucket 7 contains 1 elements.
Bucket 8 contains 1 elements.
Bucket 9 contains 1 elements.
Bucket 10 contains 1 elements.
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