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operator==,!=(std::unordered_multiset)

template< class Key, class Hash, class KeyEqual, class Alloc >
bool operator==( const std::unordered_multiset<Key, Hash, KeyEqual, Alloc>& lhs, 
                 const std::unordered_multiset<Key, Hash, KeyEqual, Alloc>& rhs );
(1)
template< class Key, class Hash, class KeyEqual, class Alloc >
bool operator!=( const std::unordered_multiset<Key, Hash, KeyEqual, Alloc>& lhs, 
                 const std::unordered_multiset<Key, Hash, KeyEqual, Alloc>& rhs );
(2) (until C++20)

Compares the contents of two unordered containers.

The contents of two unordered containers lhs and rhs are equal if the following conditions hold:

  • lhs.size() == rhs.size()
  • each group of equivalent elements [lhs_eq1, lhs_eq2) obtained from lhs.equal_range(lhs_eq1) has a corresponding group of equivalent elements in the other container [rhs_eq1, rhs_eq2) obtained from rhs.equal_range(rhs_eq1), that has the following properties:

The behavior is undefined if Key is not EqualityComparable.

The behavior is also undefined if hash_function() and key_eq() do (until C++20)key_eq() does (since C++20) not have the same behavior on lhs and rhs or if operator== for Key is not a refinement of the partition into equivalent-key groups introduced by key_eq() (that is, if two elements that compare equal using operator== fall into different partitions).

The != operator is synthesized from operator==.

(since C++20)

Parameters

lhs, rhs - unordered containers to compare

Return value

1) true if the contents of the containers are equal, false otherwise
2) true if the contents of the containers are not equal, false otherwise

Complexity

Proportional to ΣSi2 calls to operator== on value_type, calls to the predicate returned by key_eq, and calls to the hasher returned by hash_function in the average case, where S is the size of the ith equivalent key group. Proportional to N2 in the worst case, where N is the size of the container. Average case becomes proportional to N if the elements within each equivalent key group are arranged in the same order (happens when the containers are copies of each other).

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https://en.cppreference.com/w/cpp/container/unordered_multiset/operator_cmp