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unordered_set reserve() function in C++ STL

Last Updated : 7 Jun, 2023

The unordered_set::reserve() method is a builtin function in C++ STL which is used to request capacity change of unordered_set. It sets the number of buckets in the container to contain at least n elements. If n is greater than the current bucket_count multiplied by the max_load_factor, the container's bucket_count is increased and a rehash is forced. If n is lower than the bucket_count, then the function has no effect on it. 

Syntax:

unordered_set_name.reserve(size_type n)

Parameter: The function accepts a single mandatory parameter n which sets the number of buckets in the container (bucket_count) to the most appropriate to contain at least n elements. 

Return Value: This function doesn't returns anything. 

Below programs illustrate the unordered_set::reserve() function: 

Program 1: 

Output:
geeksforgeeks users geeks for

Program 2: 

Output:
for geeks

Time complexity: O(N)
 

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