# Questions tagged [hashing]

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### What exactly (and precisely) is “hash?”

I have heard the word "hash" being used in different contexts (all within the world of computing) with different meanings. For example, in the book Learn Python the Hard Way, in the chapter on ...
3answers
147 views

### Can we remove duplicates faster than we can sort?

The problem is (integer) duplicate removal, which can also be perceived as producing the image of an evaluated function (of integers): Given a sequence $S_\text{in}$ of $n$ integers, produce a ...
1answer
167 views

### Two definitions of universal hash functions

I have seen two definitions of universal hash functions in the literature. For any $i \geqslant 2$ let $[i]=\{1,\ldots,i\}$. Definition 1: A family $\mathcal H$ of hash functions from $[n]$ to ...
4answers
10k views

### Two-way Hash Functions

While I'm aware most (good) hash functions are one-way (or at least mostly so), I'm wondering if there's any construct (not necessarily called a hash function) which behaves in many ways like a hash ...
1answer
91 views

### Lemma 2 in Knuth's “Notes on Open Addressing”

I'm trying to read Knuth's Notes on Open Addressing, and I don't quite follow the proof of Lemma 2. The set-up We're thinking about hashing $k - 1$ keys into a size $N$ array, with collision ...
1answer
385 views

### Is FKS hashing really linear space?

In FKS hashing, I wonder if the size of the table $G[ 1..n]$ (used to record the functions $g_i$ which is chosen randomly; one entry per bucket) is really strictly $O(n)$. Given that the probability ...
1answer
205 views

### What is the complexity class of solving hash decision problems?

With $hash_n$, I mean a standard cryptographic hash like sha256, scaled up to have arbitrary length $n$ of its output with the same underlying principles. What is the time complexity class of the ...
0answers
223 views

2answers
63 views

### Simple Uniform Hashing Assumption and worst-case complexity for hash tables

My question: Is the Simple Uniform Hashing Assumption (SUHA) sufficient to show that the worst-case time complexity of hash table lookups is O(1)? It says in the Wikipedia article that this ...
1answer
29 views

### What are the k-collections described in ch. 8 of “An Introduction to the Analysis of Algorithms” by Sedgewick

In chapter eight of "An Introduction to the Analysis of Algorithms" by Sedgewick (1996 edition) the coupon collector problem is introduced on page 425. My confusion is how to identify the k-...
1answer
36 views

### additive hash function

Do functions with the following properties exists for x being arbitrary stream of bytes: op(f(x1), f(x2))=f(x1+x2) and op(f(x1), f(x2))!=f(x2+x1) given that x1!=x2 where plus denotes concatenation ...