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What is the fastest way to figure out if an unordered_map container has an item with a specified key?
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Return values: If the given key exists in unordered_map it returns an iterator to that element otherwise it returns the end of the map iterator. // find function in unordered_map. Time Complexity : O(1) on average.
For the unordered_map + map , it takes 70 ms for unordered_map insertion and 80 ms for map insertion. So the hybrid implementation is 50 ms faster.
How to test unordered_map is faster than map ? Note1: Let your hash function H(V) , it is better that H(V) returns distinct value for every distinct V , it makes unordered_map faster; but if you can't do that it doesn't problem.
The unordered_map::count() is a builtin method in C++ which is used to count the number of elements present in an unordered_map with a given key.
They will have about equal performance. You should use the algorithm that best expresses what you are trying to do.
To elaborate on that, generally count() will be implemented using find(). For example, in libcxx, count() is implemented as return (find(__k) != end());
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