Questions tagged [hashing]

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Mean and variance of number of buckets of length $i$ in hashing with chaining

Consider a hash table with $m$ buckets, with chaining as collision resolution policy. Given the set $S$ that will be stored in the hash table, let $X_i$ be the number of buckets whose chain length is $...
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52 views

Probability of colisson for classes of hash functions

I am going through some old exams in one of my courses, and I don't have access to solutions. I've found a problem which I am not sure how to tackle. I am not looking for the answer but some help/...
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0answers
187 views

Time complexity of obtaining the set of distinct elements in a sequence?

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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1answer
53 views

Static Perfect Hashing - FKS

I am trying to understand perfect hashing aka FKS, but I have a few questions. From my understanding, perfect hashing is a two level hashing in which you take a hash function from a universal family ...
2
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0answers
38 views

Find a non-minimal sequence of elements covering the support set

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). Denote $\text{...
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1k views

Open hashing vs closed hashing

What are advantages of closed hashing over open hashing? I know the difference between those two but can't figure out why would closed hashing be better in any way. Thanks.
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38 views

In perfect hashing, why does a secondary hash table that is quadratic in size leads to no collisions?

See below a screenshot from CLRS 3rd Edition (Section 11.5, "Perfect Hashing"). The last sentence of the last paragraph says that the choice of $m_j = n^2_j$ leads to collision-free constant-time ...
1
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1answer
24 views

Universal hashing - insert / search / delete

I don't understand the highlighted text below in CLRS 3rd Ed.: I'm not sure I even understand what the sentence is trying to say. For example: What do they mean by "... operations containing $\...
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0answers
25 views

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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35 views

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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13 views

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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100 views

Bloom filters vs storing hashes as numbers

In competitive programming there is a trick for storing a set of strings(or objects really) to reduce memory - you only keep the hashes of the strings in a hash-table (usually as 32 or 64 bit integers)...
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31 views

Time complexity of finding duplicates across multiple lists using hashing

If I have m lists with n elements each, how would I go about finding duplicates in them (i.e. an element is in more than one of the lists)? My idea is to use hashing on the elements inside the list, ...
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73 views

Checking whether a given Hashing Function fulfills Uniform Hashing Condition

I am learning about Hashing and have struggles with the following assignment: $U$ is a universe of keys with $Z(m)=\{0,\ldots, m-1 \}$ the amount of possible hash-values. Given $U= \mathbb{Z}...
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learning the private key by reusing same random variable k in ELgamal

i wonder: if for some reason, someone, say alice, sends unencrypted messages to bob and signs it using elgamal signature, can oscar,the adversary, gain knowledge of the private key if alice reused the ...
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8 views

Creating a specific hash setup

While solving a practice exam, this is the question I could not answer. Any help is appreciated. I am new to hashing and have no idea how to solve this question. Let $H$ be a $(0.15, 0.85, 0.9, 0.1)$-...
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34 views

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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33 views

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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170 views

Proof of expected number of probes in an unsuccessful search (open addressing hashing)

I'm seeking some clarification on the proof of the expected number of probes in an unsuccessful search in open addressing hashing. The proof is given in CLRS on page 275, section 11.4 (Open addressing)...
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1k views

Rolling Hash calculation with Horner's method

I understood how Horner's method reduces the complexity(number of operations) while evaluating a polynomial. I have a character array derived from a string ...
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44 views

Verification of extendible hashing proof

I have to proof this theorem: "An extendible hashing table always contains at least one bucket where only one pointer points to after an element is added". I made this proof, but I'm not completely ...