# Questions tagged [hashing]

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### Linear probing and tabulation hashing

I'm currently reading the paper "The Power of Simple Tabulation Hashing" by Mihai Patrascu and Mikkel Thorup [1] because I want to adapt the proof of the constant time complexity of linear probing for ...
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### 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 ...
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### Structure Preserving Continuous Hash Function

This question was originally posted on super user, but redirected here based on some suggestions. I am completely new with computer science, and not only recently did I run into the notion of hashing....
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### What is the deterministic time complexity of obtaining the set of distinct elements?

Consider a sequence $s$ of $n$ integers (let's ignore the specifics of their representation and just suppose we can read, write and compare them in O(1) time with arbitrary positions). What's known ...
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### Given a family of hash functions in table form, how can I know whether it's universal?

I've been given the following two families of hash functions: H and G Each family has three functions $\{0,1,2,3,4\} \to \{0,1,2\}$ that can be seen in the tables above. For each family I need to ...
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### While computing signature matrix in min hashing, can I take nth row of the permutation P in which document d has value 1?

I am learning about some techniques to find similarity between documents. One of the methods is Min Hashing. According to Min Hashing we can find a signature matrix given a random permutation, P. ...
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### Construction of hash function with a given distribution

Two questions about the construction of a hash function: Let $U = \{u_1,...,u_n\}$ be a set of size $n$, and suppose that one is interested in a function $h\colon U \rightarrow [0,1]$ such that $h$ "...
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### The expectation of the total number of pairs of keys in a hash table that collide using universal hashing

I am reading CLRS relating to perfect hashing. When computing the $$\mathbb{E}[\sum_{j=0}^{m-1}{n_j\choose{2}}]$$ where $m$ is the number of slots in the hash table, and $n_j$ is the number of keys ...
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### How does Rabin fingerprint finds breakpoints (chunk boundary)?

I was reading up on chunking and found Rabin fingerprinting is also used to break files into chunks. After reading about this algorithm, I understood how rolling hash is computed using Rabin ...
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### is modulo of hash function is evenly distributed?

if I take the result of a 32bit hash function(the param is random string) and apply module N on the result - will the values be evenly distributed? so if I have a histogram of values [0,N-1] will the ...
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### Check whether all elements are different

Assume we have $n$ double elements $a_1 \dots a_n$. We want to find out if two of the elements of the array are identical. And we have a hash function $h(x)$ which assigns each double value an integer ...
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### Does this excerpt from the linear probing Wikipedia page make an assumption?

Here is the excerpt from the linear probing page at Wikipedia. To search for a given key x, the cells of T are examined, beginning with the cell at index h(x) (where h is the hash function) and ...
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### 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-...
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### Probability in 1-universal hash function

I am trying to prepare for an exam and I am not sure how to solve this task: Given is a hash function with m buckets, which uses a 1-universal hash function h: U -> H and handles collisions with ...
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### Search operation in hash table

Suppose that we have a hash table of some size $s$ and we have a set of keys $K$. We decide to hash the keys using chaining. Now assume that we randomly select $k \in \mathbb{N}$ keys from $K$ and ...
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### Ketama hash explanation

(I originally posted this on stackoverflow but thought it would be a better fit here) I'm trying to understand the Ketama hash code used in consistent hashing. link and snippet below: ...
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### Dynamic Perfect Hashing and Lower Bound

I am writing a Seminar about dynamic perfect hashing and its lower bound by the FKS schema using the the adversary method mentioned here by using a Tree data structure. But somehow i don t get how ...
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### Is there a running hash algorithm that can efficiently handle arbitrary updates to a file's contents?

This question is about file-hashing/fingerprinting algorithms (similar to SHA-1 and MD5 and so on). Those algorithms are handy ...
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### 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 ...
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### Is there a way to theoretically compare hash functions?

Say I am given two hash functions f1 and f2 is there anyway that I can prove one hash function will produce fewer collisions ...
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### Unique ID from date and rotating offset

Hopefully this is the right board for my question, We are facing an issue creating a unique ID from the following inputs : datetime (can be present more than once in the same set, cannot not be ...
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### General name for linked lists based on hashes

I am thinking of a particular datastructure, but don't know the name of it. A sequence of elements may be modeled by a collection of some X, where each X consists of: The element, serialized as a ...