# Tag Info

Accepted

### What exactly (and precisely) is "hash?"

The Wikipedia article on hash functions is very good, but I will here give my take. What is a hash? "Hash" is really a broad term with different formal meanings in different contexts. There ...

### What exactly (and precisely) is "hash?"

A hash function is a function that takes an input and produces a value of fixed size. For example you might have a hash function stringHash that accepts a ...
Accepted

### Two-way Hash Functions

Yes, this is possible. Here are two examples of such a function. One function is $f(x)=x$. This has no collisions, and the function is easy to invert. Here is another function: define $f(x) = x$ ...
Accepted

### Hash functions and pathological data sets

An easy way to visualize this is to imagine a hash table of size $n$ (implemented with chaining) that contains all of the elements of $U$ (even though this is unrealistic in practice because $U$ ...
Accepted

### Understanding hashtable performance in the worst-case

The load factor denotes the average expected length of a chain, therefore it is interesting for an average case analysis, not the worst case analysis. That's why on average you expect needing constant ...

### Hash function to hash 6-digit positive integers

I think you've missed the point of hash tables. Hash tables are used to give array-like access to a dataset that's too big and sparse to store in an array. So, for example, it sounds like you're ...
Accepted

### Given a string, is it possible to determine which hashing algorithm has produced it, if any?

You will first need to define what you mean by a hashing algorithm. For example, my favorite hashing algorithm is simple: check whether the input is "string", and if so, output "...

### Given a string, is it possible to determine which hashing algorithm has produced it, if any?

No it is not possible to determine that is produced by a hashing algo, or which one that produced it -- at least not from a single sample. Good hashing algo will produce a uniform set of values ...

### Two-way Hash Functions

In addition to everything that others have said: any cipher is an invertible "hash" function. And there are standard ways to construct them; one common way of turning a one-way function into an ...