C++ unordered_map::bucket_count() 函数



C++ 函数unordered_map::bucket_count()返回容器中桶的数量。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)。

语法

以下是 std::unordered_map::bucket_count() 函数的语法。

size_type bucket_count() const noexcept;

参数

此函数不接受任何参数。

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返回值

返回 unordered_map 中存在的桶的总数。

示例 1

考虑以下示例,我们将观察 unordered_map::bucket_count() 函数的用法。

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} }; cout << "Number of buckets = " << um.bucket_count() << endl; return 0; }

输出

以下是上述代码的输出:

Number of buckets = 13

示例 2

在下面的示例中,我们使用 bucket_count() 获取 unordered_map 中桶的总数以及每个桶中的项目数量。

Open Compiler
#include <iostream> #include <string> #include <unordered_map> using namespace std; int main () { unordered_map<string, string> UnorderMap={ {"Aman","Akash"}, {"Gautam","Garav"}, {"Anil","Sunil"}, {"Raja","Roja"}, {"Sarika","Revathi"}, }; unsigned n = UnorderMap.bucket_count(); cout << "map has " << n << " buckets.\n"; for (unsigned i=0; i<n; ++i) { cout << "bucket #" << i << " contains: "; for (auto it = UnorderMap.begin(i); it!=UnorderMap.end(i); ++it) cout << "[" << it->first << ":" << it->second << "] "; cout << "\n"; } return 0; }

输出

以下是上述代码的输出:

map has 13 buckets.
bucket #0 contains: 
bucket #1 contains: 
bucket #2 contains: 
bucket #3 contains: [Raja:Roja] 
bucket #4 contains: 
bucket #5 contains: [Anil:Sunil] [Gautam:Garav] 
bucket #6 contains: 
bucket #7 contains: 
bucket #8 contains: [Aman:Akash] 
bucket #9 contains: [Sarika:Revathi] 
bucket #10 contains: 
bucket #11 contains: 
bucket #12 contains: 

示例 3

考虑以下示例,我们使用 [] 运算符创建 unordered_map,并使用 bucket_count() 计数桶的数量,使用 buckets_size() 计数每个桶中的元素数量。

Open Compiler
#include <iostream> #include <unordered_map> using namespace std; int main() { unordered_map<char, int> umap; umap['a'] = 1; umap['b'] = 2; umap['c'] = 3; umap['d'] = 4; umap['e'] = 5; int n = umap.bucket_count(); cout << "umap has " << n << " buckets.\n\n"; // Count no. of elements in each bucket using // bucket_size(position) for (int i = 0; i < n; i++) { cout << "Bucket " << i << " has "<< umap.bucket_size(i) << " elements.\n"; } return 0; }

输出

让我们编译并运行上面的程序,这将产生以下结果:

umap has 13 buckets.

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