Questions tagged [hashtable]

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1answer
74 views

how to store the data for function f(time,length)

I have a function which has discrete time step ,discrete length from origin . These two give height of the function. For example at time 1.2sec , and length 5.5cm from origin height is 10cm. The step ...
0
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1answer
529 views

What is the space complexity of a Python dictionary?

If python dictionaries are essentially hash tables and the length of hashes used in the python dictionary implementation is 32 bits, that would mean that regardless of the number of key-value pairs ...
2
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2answers
122 views

Load factor and prime number for hashing in HashTable

I am trying to design a HashTable from scratch. I am starting with an initial bucket size of 11 and trying to maintain a load factor 0.75. Java documentation mentions that whenever the number of ...
6
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5answers
2k views

Implementing a hash table with true concurrency

This was recently a question I was asked in a screening and it got me thinking. I never totally settled on how the conversation ended, and I did some digging. None of the answers I saw seemed ...
0
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0answers
86 views

Searching/Hashing Wikipedia - at each position for keys 1..31 long, the fastest way?

A C coder here. My wish is to find the best way to search words and phrases within the ever-growing English Wikipedia XML dump. As a first layer/step, hashing is the answer, yes? The problem is that ...
1
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1answer
74 views

Library with different runtime behaviour based on usage history (design question) [closed]

I want to design a hash table library that keeps usage statistics and based on how it is used will use different implementations at runtime. For example use a certain implementation for small size ...
3
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0answers
59 views

java hashtable extending to support duplicates

I have to maintain an old application and have to extend some modules. There is an hashtable that is used for maintaining/holding some objects as representation of running (real) processes (don't see ...
0
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1answer
403 views

Logic Behind a Basic Hash Table Hashing Algorithm

I am trying to write a Hash Table in Java based on some Princeton article about it. The most commonly used method for hashing integers is called modular hashing: we choose the array size M to be ...
2
votes
2answers
4k views

How exactly indexing works in arrays?

I only know that index is faster but don't know why is it faster. Suppose I have an array int[] a = {2,3,6,7}. Then I will try to find the element at a[3] and the speed of this will be O(1). Why? How ...
1
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0answers
130 views

speed up search in string array [closed]

Suppose we have sorted array of strings e.g. std::vector<std::string> or some other elements with string as key - for example std::vector<std::pair<std::string,data_type>. Normally to ...
3
votes
1answer
791 views

Hash Table with iterators as the keys, is this poor design and can I do this better?

I'm developing a program where twice I've found the solution to a problem was to use hash tables with iterators as keys and some other arbitrary type as the value. I found my self using this pattern ...
0
votes
1answer
115 views

What is the opposite of the 'load factor' (in reference to hash tables)

When the load of the hash table grows too large in proportion to the hash table size, you increase the size of the hash table to improve performance. When the load is too large is dependant on a ...
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3answers
274 views

What can I infer from Hilbert's map?

How do I understand Hilbert's map in this answer? The author of the answer has mapped the hash value (integer) of some strings to a 2D image. I understand that Hilbert's curve is a technique for 1D &...
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2answers
691 views

Can hashtable be used for implementing multimap?

Is it correct that hashtables assume no key is shared between more than one records? In other words, can hashtables be used for implementing multimaps? When using a hashtable, can't multiple records ...
1
vote
3answers
296 views

Can a hash table implement a relation which can't be viewed as a mapping?

A (partial or total) mapping from set S to T is a special relation between S and T. The difference between a mapping and a relation is that: a relation between S and T in general doesn't require that ...
3
votes
1answer
283 views

When should a general purpose hash table assume hash equality implies logical equality?

For a general purpose hash table that aims for both high performance and correctness, when, if ever, does it make sense to assume that hash equality implies logical equality? To lay some ground rules ...
0
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0answers
47 views

Reverse lookup of data based on user input

I have an array in the format: $array = array( 0 => array( 'name' => 'Item 1', 'level' => 1, 'points' => 10 ), 1 => array( 'name' => '...
4
votes
1answer
689 views

How does cuckoo hashing guarantee O(1) lookups in presence of persistent hash collisions

Most hash table implementations guarantee O(1) average case but O(n) maximum case for lookup (where 'n' is the number of keys in the table). But Cuckoo Hashing is described as O(1) maximum. ...
51
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4answers
51k views

What is the difference between a hash and a dictionary?

What is the difference between Hash and Dictionary? Coming from a scripting background, I feel that they are similar, but I wanted to find out the exact differences. Googling did not help me much.