std::unordered_multiset<Key,Hash,KeyEqual,Allocator>::equal_range
From cppreference.com
< cpp | container | unordered multiset
|
std::pair
<iterator, iterator> equal_range(
const Key& key )
;
|
(1) | (since C++11) |
|
std::pair
<const_iterator, const_iterator> equal_range(
const Key& key )
const
;
|
(2) | (since C++11) |
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template
<
class K >
std::pair <iterator, iterator> equal_range( const K& x ) ; |
(3) | (since C++20) |
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template
<
class K >
std::pair <const_iterator, const_iterator> equal_range( const K& x ) const ; |
(4) | (since C++20) |
1,2) Returns a range containing all elements with key
key
3,4) Returns a range containing all elements in the container with key equivalent to x. This overload participates in overload resolution only if Hash::is_transparent and KeyEqual::is_transparent are valid and each denotes a type. This assumes that such
Hash is callable with both K and Key type, and that the KeyEqual is transparent, which, together, allows calling this function without constructing an instance of Key
Parameters
| key | - | key value to compare the elements to |
| x | - | a value of any type that can be transparently compared with a key |
Return value
std::pair containing a pair of iterators defining the wanted range. If there are no such elements, past-the-end (see end()
Complexity
Average case linear in the number of elements with the key key, worst case linear in the size of the container.
Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_generic_unordered_lookup |
201811L |
(C++20) | Heterogeneous comparison lookup in unordered associative containers, overloads (3,4) |
Example
Estimates the characters frequency for given string.
Run this code
#include <iostream> #include <iterator> #include <string> #include <unordered_set> int main() { std::string sentence{"cppreference.com"}; std::cout << "The sentence: " << sentence << '\n'; std::unordered_multiset<char> sequence; for (char x : sentence) sequence.insert(x); std::cout << "The sequence: { "; for (char x : sequence) std::cout << x << ' '; std::cout << "}\n" "Symbol:Frequency: "; for (auto it = sequence.begin(); it != sequence.end();) { if (auto [first, last] = sequence.equal_range(*it); first != last) { std::cout << *first << ":" << std::distance(first, last) << " "; it = last; } else ++it; } }
Possible output:
The sentence: cppreference.com
The sequence: { m o c c c p p r r e e e e f n . }
Symbol:Frequency: m:1 o:1 c:3 p:2 r:2 e:4 f:1 n:1 .:1See also
| finds element with specific key (public member function) |
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(C++20)
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checks if the container contains element with specific key (public member function) |
| returns the number of elements matching specific key (public member function) |
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| returns range of elements matching a specific key (function template) |