ConcurrentHashMap and Hashtable locking mechanism Hashtable is belongs to the Collection framework; ConcurrentHashMap belongs to the Executor framework. Hashtable uses single lock for whole data. ConcurrentHashMap uses multiple locks on segment level (16 by default) instead of object level i.e. whole Map. ConcurrentHashMap locking is applied only for updates. In case of retrievals, it allows … Read more
I would recommend you to try Google SparseHash (or the C11 version Google SparseHash-c11) and see if it suits your needs. They have a memory efficient implementation as well as one optimized for speed. I did a benchmark a long time ago, it was the best hashtable implementation available in terms of speed (however with … Read more
I think you are looking for the Dictionary object, found in the Microsoft Scripting Runtime library. (Add a reference to your project from the Tools…References menu in the VBE.) It pretty much works with any simple value that can fit in a variant (Keys can’t be arrays, and trying to make them objects doesn’t make … Read more
Hash tables are O(1) average and amortized case complexity, however it suffers from O(n) worst case time complexity. [And I think this is where your confusion is] Hash tables suffer from O(n) worst time complexity due to two reasons: If too many elements were hashed into the same key: looking inside this key may take … Read more
Shorthand is not preferred for scripts; it is less readable. The %{} operator is considered shorthand. Here’s how it should be done in a script for readability and reusability: Variable Setup PS> $hash = @{ a = 1 b = 2 c = 3 } PS> $hash Name Value —- —– c 3 b 2 … Read more
Here is a class for a bidirectional dict, inspired by Finding key from value in Python dictionary and modified to allow the following 2) and 3). Note that : The inverse directory bd.inverse auto-updates itself when the standard dict bd is modified. The inverse directory bd.inverse[value] is always a list of key such that bd[key] … Read more
Hash tables deal with collisions in one of two ways. Option 1: By having each bucket contain a linked list of elements that are hashed to that bucket. This is why a bad hash function can make lookups in hash tables very slow. Option 2: If the hash table entries are all full then the … Read more
One advantage that no one else has pointed out is that binary search tree allows you to do range searches efficiently. In order to illustrate my idea, I want to make an extreme case. Say you want to get all the elements whose keys are between 0 to 5000. And actually there is only one … Read more
If you are on .NET 4.0 use a Tuple: lookup = new Dictionary<Tuple<TypeA, TypeB, TypeC>, string>(); If not you can define a Tuple and use that as the key. The Tuple needs to override GetHashCode, Equals and IEquatable: struct Tuple<T, U, W> : IEquatable<Tuple<T,U,W>> { readonly T first; readonly U second; readonly W third; public … Read more
You have two variables here, m and n, where m is the length of the input and n is the number of items in the hash. The O(1) lookup performance claim makes at least two assumptions: Your objects can be equality compared in O(1) time. There will be few hash collisions. If your objects are … Read more