HashSet 中的哈希性能<int>针对列表<int>包含</int></int>

Question

I am looking for a comparison/performance considerations between a list of integers against a hash set of integers . This is what What is the difference between HashSet<T> and List<T>? talks about for T as integer.

I will have up to several thousand integers, and I want to find out, for individual integers, whether they are contained in this set.

Now of course this screams for a hash set, but I wonder whether hashing is beneficial here, since they are just integers to start with. Would hashing them first not add unnecessary overhead here?

Or in other words: Is using a hash set beneficial, even for sets of integers?

Answer 1

Hashing an integer is very cheap, as you can see in the source code of the Int32.GetHashCode method:

// The absolute value of the int contained.
public override int GetHashCode()
{
    return m_value;
}

The hash of the number is the number itself. It can't get any cheaper than that. So there is no reason to be concerned about the overhead. Put your numbers in a HashSet , and enjoy searching with O(1) computational complexity.

Answer 2

What ever T is there is a simple but efficient rule of thumb:

• The collection is mainly used for adding and iterating with very few search => Use List

• The collection is heavely used for research => Use HashSet