# Questions tagged [hash-tables]

A finite map data structure that addresses stored values using a function that maps many values to few addresses.

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### Detecting and correcting collisions in (Zorbist) hashing to avoid errors in transposition table

Context Say I have a transposition table that uses keys produced by (e.g. Zorbist) hashing game positions. The table has a finite recycled memory (key % p is the <...
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### Number of unique values in array in $\theta(n)$ average expected time

My idea is to initialize a hash table (with chaining) with $n$ cells, having load factor $\alpha = 1$ hence having $\theta(1)$ expected number of values in each cell in the hash table, then go cell by ...
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### The Most efficient algorithm for a program that returns true if the two strings only differ by one character

We have a list of strings with the same length. Each string only contains a, b and c.(For instance : aabcc) The program gets a string and returns true if the two strings(input and the list of strings) ...
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### Counting distinct elements in array using hash table and measuring efficiency

I need to implement an algorithm to solve the Count-distinct problem given an array of $N$ elements using a hash table, and devise metrics with which to measure my algorithm efficiency. I was told I ...
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### What kind of data structure should be used for working with dynamic sets where elements follow “normal distribution” and why?

I am wondering if Hash tables would be a good choice as it mentions dynamic sets to store data which follows normal distribution. I have doubt in this because normal distribution has bell shaped curve ...
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### Find distinict elements in an array in $O(n)$ time

Given this pseudo-code that finds the number of distinct elements in the given array: ...
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### Finding the longest power subsequence

A power sequence is a sequence containing consecutive powers of a number starting from power one. for example $3^1, 3^2, 3^3$ is a power sequence. The question is to find the length of the longest ...
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### Time complexity of checking whether a string exists in a HashSet

From what I know hash sets generally have complexity of $O(1)$ (unless the hash function is bad, but let's just ignore that for this question). However, sets need to either read the full data so as to ...
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### How do we pick and switch hash functions from a universal family?

When we have a universal family of hash functions, it gives us a few useful mathematical guarantees. But, if we pick a specific function from the family and use it all the time it's effectively like ...
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### Hash tables for storing data in an application that supports partial search

Is a hash table a good data structure for storing data in an application that support partial search such as "select * from MyTable where name like 'John%'. If not, what is? I would have thought ...
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### Error handling in a size_t hashfunction

For school I have a big assignment on hashtables etc. One of the functions is a size_t function where we calculate the hash value. (Keep in mind the structure of every function is given so we are not ...
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### How to generate unique keys for different two dimensional matrices having different sizes?

No. of rows in the table (as given in image) is not known beforehand . The problem I am dealing with generates different 2-D matrices based on the input data given. As soon as a matrix generates it ...
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### What is the best of given hashfunctions?

In our exam on algorithms there was a question, where given 3 hashfunctions we had to chose one and explain why it's the best. h_1(x,i)=(x+5*i) mod 1000 h_2(x,i)=(x+17*i) mod 1000 h_3(x,i)=(x+32*i) ...