C++ unordered_multimap::bucket() 函式

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C++ 的std::unordered_multimap::bucket()函式用於返回包含鍵為k的元素所在的桶號。

桶是容器雜湊表中的一個記憶體空間，元素根據其鍵的雜湊值分配到該記憶體空間。桶的大小範圍是0到bucket_count-1。

語法

以下是std::unordered_multimap::bucket()函式的語法。

size_type bucket(const Key& keyval) const;

引數

• k - 表示要查詢其桶的鍵。

返回值

此函式返回無符號整型，表示對應於鍵的桶的序號。

示例 1

在以下示例中，讓我們看看unordered_multimap::bucket()函式的使用方法。

#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;
}

輸出

讓我們編譯並執行上述程式，這將產生以下結果：

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

讓我們看下面的例子，我們將建立一個儲存字串值的unordered_multimap，並應用bucket()函式來統計彼此分配的桶的數量。

#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;
}

輸出

如果我們執行上面的程式碼，它將生成以下輸出：

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

考慮以下示例，我們將顯示從unordered_multimap指向容器第一個元素的迭代器的桶數。

#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;
}

輸出

以下是上述程式碼的輸出：

The bucket number of key Akash is 4

示例 4

以下是一個示例，我們將顯示當前unordered_multimap中指定鍵的桶號。

#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;
}

輸出

以上程式碼的輸出如下：

10
2