I’m looking for an explanation of how a hash table works – in plain English for a simpleton like me! For example, I know it takes the key, calculates the hash (I am looking for an explanation how) and then performs some kind of modulo to work out where it lies in the array where … Read more
Section 6.6 of The C Programming Language presents a simple dictionary (hashtable) data structure. I don’t think a useful dictionary implementation could get any simpler than this. For your convenience, I reproduce the code here. Note that if the hashes of two strings collide, it may lead to an O(n) lookup time. You can reduce the likelihood of collisions … Read more
It depends on many things. It’s usually O(1), with a decent hash which itself is constant time… but you could have a hash which takes a long time to compute, and if there are multiple items in the hash map which return the same hash code, get will have to iterate over them calling equals on each of them to find a match. … Read more
A list keeps order, dict and set don’t: when you care about order, therefore, you must use list (if your choice of containers is limited to these three, of course 😉 ). dict associates each key with a value, while list and set just contain values: very different use cases, obviously. set requires items to be hashable, list doesn’t: if you have non-hashable items, therefore, you cannot use set and must instead use list. … Read more
Yes. Set a reference to MS Scripting runtime (‘Microsoft Scripting Runtime’). As per @regjo’s comment, go to Tools->References and tick the box for ‘Microsoft Scripting Runtime’. Create a dictionary instance using the code below: or Example of use: Don’t forget to set the dictionary to Nothing when you have finished using it.
It depends on what you are intending to do with it. Sets are significantly faster when it comes to determining if an object is present in the set (as in x in s), but are slower than lists when it comes to iterating over their contents. You can use the timeit module to see which is faster for … Read more
A cut of a connected graph is a minimal set of edges whose removal separate the graph into two components (pieces). The minimal cut property says that if one of the edges of the cut has weight smaller than any other edge in the cut then it is in the MST. To see this, assume … Read more
Python includes the heapq module for min-heaps, but I need a max heap. What should I use for a max-heap implementation in Python?
For what it’s worth, a Dictionary is (conceptually) a hash table. If you meant “why do we use the Dictionary<TKey, TValue> class instead of the Hashtable class?”, then it’s an easy answer: Dictionary<TKey, TValue> is a generic type, Hashtable is not. That means you get type safety with Dictionary<TKey, TValue>, because you can’t insert any random object into it, and you don’t have to cast the … Read more
Java definitively has no structs 🙂 But what you describe here looks like a JavaBean kind of class.