C++ unordered_multimap::bucket() 函数

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C++ 的std::unordered_multimap::bucket()函数用于返回包含键为k的元素所在的桶号。

桶是容器哈希表中的一个内存空间，元素根据其键的哈希值分配到该内存空间。桶的大小范围是0到bucket_count-1。

语法

以下是std::unordered_multimap::bucket()函数的语法。

size_type bucket(const Key& keyval) const;

参数

• k - 表示要查找其桶的键。

返回值

此函数返回无符号整型，表示对应于键的桶的序号。

示例 1

在以下示例中，让我们看看unordered_multimap::bucket()函数的使用方法。

#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}
   };
   cout << "Unordered multimap contains following elements" << endl;
   for (auto it = umm.begin(); it != umm.end(); ++it) {
      cout << "Element " << "[" << it->first  << " : "<< it->second << "] " << "is in " << umm.bucket(it->first) << " bucket." << endl; 
   }
   return 0;
}

输出

让我们编译并运行上述程序，这将产生以下结果：

Unordered multi-map contains following elements
Element [e : 5] is in 1 bucket.
Element [d : 4] is in 0 bucket.
Element [c : 3] is in 4 bucket.
Element [b : 2] is in 3 bucket.
Element [a : 1] is in 2 bucket.

示例 2

让我们看下面的例子，我们将创建一个存储字符串值的unordered_multimap，并应用bucket()函数来统计彼此分配的桶的数量。

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void) {
   unordered_multimap<string, string> umm = {
      {"Aman", "Ranchi"},
      {"Vivek", "Kanpur"},
      {"Akash", "Daltonganj"},
      {"Aman", "Ranchi"},
      {"Vivek", "Kanpur"},
   };
   for (auto it = umm.begin(); it != umm.end(); ++it) {
      cout << "Element " << "[" << it->first  << " : "
      << it->second << "] " << "is in " 
      << umm.bucket(it->first) << " bucket." << endl;
   }
   return 0;
}

输出

如果我们运行上面的代码，它将生成以下输出：

Element [Akash : Daltonganj] is in 4 bucket.
Element [Vivek : Kanpur] is in 4 bucket.
Element [Vivek : Kanpur] is in 4 bucket.
Element [Aman : Ranchi] is in 3 bucket.
Element [Aman : Ranchi] is in 3 bucket.

示例 3

考虑以下示例，我们将显示从unordered_multimap指向容器第一个元素的迭代器的桶数。

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void) {
   unordered_multimap<string, string> umm = {
      {"Aman", "Ranchi"},
      {"Vivek", "Kanpur"},
      {"Akash", "Daltonganj"},
      {"Aman", "Ranchi"},
      {"Vivek", "Kanpur"},
   };
   // prints the bucket number of the beginning element
   auto it = umm.begin();
   // stores the bucket number of the key k
   int number = umm.bucket(it->first);
   cout << "The bucket number of key " << it->first << " is " << number;
   return 0;
}

输出

以下是上述代码的输出：

The bucket number of key Akash is 4

示例 4

以下是一个示例，我们将显示当前unordered_multimap中指定键的桶号。

#include <iostream>
#include <unordered_map>
using namespace std;
int main(void) {
   unordered_multimap<char, int> umm = {
      {'A', 1},
      {'B', 2},
      {'C', 3},
      {'A', 1},
      {'D', 4},
      {'A', 1},
      {'E', 5},
      {'D', 4},
   };
   cout<<umm.bucket('A')<<endl;
   cout<<umm.bucket('D')<<endl;
   return 0;
}

输出

以上代码的输出如下：

10
2