Questions tagged [dictionaries]
The dictionaries tag has no usage guidance.
52
questions
1
vote
2
answers
37
views
Dictionary with sets as keys where lookup can be set intersection
Normally, when working with dictionaries, we expect around O(1) complexity when we go to retrieve a value given the key (and when we insert). I work in Python, but this might apply to any dynamic ...
- 11
0
votes
0
answers
22
views
Unusual approach to tabulation algorithm
Consider simple tabulation algorithm firstly for Fibonacci numbers.
We will use the dictionary as a cache (and Python as example PL):
...
- 101
1
vote
1
answer
84
views
How does the Go language implements maps?
To what extent is the MAP data type implementation language dependant???
If we know that C++ implements maps as Red Black Trees, unordered maps as hash tables,
How C++ and alike maps are actually ...
- 140
0
votes
0
answers
55
views
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) ...
1
vote
1
answer
150
views
LZW with dictionary clearing
How does LZW decompress data with dictionary clearing/flushing? I understand that a space is reserved in the dictionary that represents a clear code (usually 256), but how is this code actually used ...
- 11
1
vote
0
answers
61
views
Why is sparsity useful in dictionary learning?
What is the particular reason for which we use sparse matrix X in dictionary learning equation Y=DX where Y is the signal matrix, D is dictionary and X is the coefficient matrix?
- 123
1
vote
0
answers
20
views
If statement not capturing the conditional I'm seeking [closed]
I'm working on a hw assignment, and my if statement isn't working the way it's intended.
This is an ATM machine project. I've already gotten the program to read the csv file and stored it into a ...
- 11
0
votes
1
answer
314
views
Parallel Algorithm for Data Averaging
I am trying to write an efficient Parallelised algorithm for Data Averaging. By this I mean I have a list of tuples (K, V1, V2, V3) and in the end, I want a dictionary mapping K to the average of all ...
2
votes
1
answer
726
views
Remove duplicates from dictionary in a safe and clever way
I have a dictionary that has keys and multiple values per key. Same value can be assigned to multiple keys.
For the sake of simplicity, the keys are ints and the ...
- 123
7
votes
1
answer
249
views
Most space-efficient lossy dictionary?
Short version: What is the most space-efficient lossy dictionary (with given false positive and false negative rates)?
Long version: A lossy dictionary is a data structure $D$ that encodes a set $S$ ...
- 391
1
vote
1
answer
73
views
Determining possible data structures given a set of required operations
This was an interview question that I was told is supposed to be an open ended discussion of the trade-offs.
You have a collection of comparable objects and want to be able to do the following:
1. ...
- 111
0
votes
0
answers
57
views
Dictionary matching problem: dictionary size estimation
Suppose we solve dictionary matching problem for $d$ patterns with the Aho-Corasick algorithm. Then our main data structure consists of a trie with $n$ vertices and auxiliary structures. I want to ...
- 131
3
votes
4
answers
1k
views
time efficient key value store for fast lookup
Let's state a collection of key/values.
Key is an unsigned integer (0 - 2^32-1). Hense there are comparable.
Value is few bytes fixed size.
There are 4M items in the collection.
Keys are not evenly ...
- 131
2
votes
1
answer
519
views
Algorithms to correct misspelled word?
At present, I am doing a project on Optical Character Recognition (OCR). I am looking forward to improve the results by checking the output words of my OCR code with existing words from a text file. ...
- 309
1
vote
3
answers
516
views
Match dictionary to misspelled word, corner cases
I'm trying to think of corner-cases where I can skip having to linear-search through my dictionary in my problem; For a given word w1, find all matches with the least editing distance from it in the ...
- 265
14
votes
3
answers
2k
views
Memoization without array
In Cormen et al.'s Introduction to algorithms, section 15.3 Elements of dynamic programming explains memoization as follow:
A memoized recursive algorithm maintains an entry in a table for the ...
- 311
6
votes
1
answer
623
views
Best data structure for a queue with random reads?
Well, it's not exactly a queue if it allows for random reads. This question is about a data structure which behaves like a queue for insertions and a sorted dictionary for reads.
Imagine an algorithm ...
- 239
0
votes
1
answer
364
views
What happens internally when you remove an object from a treemap
I am wondering what happens if you remove an object in the middle of a treemap.
If the treemap would look something like this:
So what would happen if you remove the number 30? Because 27 and 34 ...
Luud van Keulen
4
votes
2
answers
379
views
Fastest static associative map
Let's say that I wanted to build a key to value associative map where the only requirement was that lookup times were fast.
Once built, the associative map would not allow inserts, deletes, or ...
- 1,320
0
votes
1
answer
500
views
Complexity of testing membership in a disjoint set
I have a disjoint set data structure (sometimes known as a union-find data structure) where I store a value in each "node". I want to look up a node by value. How can I do this?
The representations ...
- 113
5
votes
1
answer
1k
views
Suggest a data-structure that supports the following operations with time complexity of $ O(log(n)) $
Iv'e been struggling a lot with this one.
I am looking for a data-structure (could be a modification of an existing type of data-structure, or a combination of more than one data-structure), which ...
- 155
3
votes
3
answers
171
views
Data structure choice for a query-update-delete problem
Given is an initial set of n keys. Each key k is of the form (p, q). Note that both p and q are positive.
At any given point, there are two possible actions:
1) Query-Delete: Given a value s as ...
- 31
1
vote
1
answer
229
views
Which in-memory data structure can accommodate billions of md5 value?
For my application, I have to store billions of md5 values, and before storing new md5 I wanna make sure that it doesn't exist already in it.
I tried using hash data structure, it worked well but no ...
- 11
2
votes
2
answers
1k
views
O(1) access into an array-like data structure with numerical ranges for keys
Preface: It's been a long time since I've been in school, and my terminology is probably all wrong. Apologies...
Summary: I have a data structure with probability ranges assigned to the elements, and ...
- 121
1
vote
2
answers
5k
views
Data structure with constant time operations
I need to use a data structure, implementable in C++, that can do basic operations, such as lookup, insertion and deletion, in constant time. I, however, also need to be able to find the maximum value ...
user35756
2
votes
1
answer
109
views
How can a set offer better search performance than an array
While reading the following tutorial on iOS development Working with Foundation (section on Sets near the bottom), I came across the following statement: "Because sets don’t maintain order, they offer ...
- 123
6
votes
3
answers
15k
views
What is the advantage of seperate chaining over open addressing?
Hash tables resolve collisions through two mechanisms,
separate chaining or open hashing and
open addressing or closed hashing.
Though the first method uses lists (or other fancier data structure) ...
- 171
6
votes
1
answer
217
views
Is it possible to implement a dictionary with efficient access according to insertion order?
I am trying to build a generic data structure that needs to hold keys and values and in the same time keep track on the indices in which keys and values were put in, like arraylists do but in a ...
- 161
1
vote
1
answer
747
views
A many-to-many mapping data structure
What would be a good way representing:
i. Given a key, return all the data values associated with that key
AND
ii. Given a data value, return all the keys that are associated with that data.
So far, ...
- 125
4
votes
1
answer
5k
views
Segment trees with insertion/deletion
I have a range query problem to solve. This problem requires not only range queries and update, but also insert or delete an element of the array. There is a series of operations that must be done in ...
- 327
2
votes
0
answers
107
views
Why can't fractional cascading be used on two unrelated arrays?
According to both Wikipedia and my professor (see question 5.1), fractional cascading has to be done on arrays with related data.
The specific question:
A fellow student wants to compactly store ...
- 121
60
votes
4
answers
18k
views
Why are Red-Black trees so popular?
It seems that everywhere I look, data structures are being implemented using red-black trees (std::set in C++, SortedDictionary ...
- 837
1
vote
1
answer
608
views
Applications of queues [closed]
Let suppose a simple (FIFO) queue, where elements enter at a side and exit at the other side.
I know the classical use of queues in everyday life and computer networking. I would like to know more ...
- 435
2
votes
3
answers
47
views
Existence of functions that only tests memberships without revealing any information about the members
Given a set of strings $\{s_1, s_2, \cdots, s_n\}$, is there a way to encode them to a program $P$, such that given some string,$s$, the program can test the membership efficiently (deterministically ...
- 1,676
-2
votes
1
answer
725
views
Find K-th next element in O(log n) time
We want to store a set S of distinct positive integers and support the following operations on S:
Insert(a): insert integer a !∈ S into S.
Delete(a): delete integer a ∈ S from S.
FindNext(a, k), where ...
- 1
0
votes
1
answer
2k
views
Selection problem on the union of two ordered dictionaries
Suppose we are given two ordered dictionaries S and T each with n items, and that S and T are implemented by means of array-based ordered sequences. Describe an O(log n) time algorithm for finding the ...
- 9
1
vote
1
answer
594
views
Data structure for range-value-sum
I have to be able to perform insert, delete, range-value-sum, and range-2-max-values with a data structure.
Range-value-sum(xl,xr): with a range [xl,xr] (for a range query), it reports the sum of ...
- 101
3
votes
2
answers
1k
views
Data structure to insert, update and sort indexes by frequency and query an index for a particular cumulative frequency
Here is the description of the data structure I am looking for:
Initial Original Data
Index | Frequency |
1 3
2 1
3 7
4 2
5 6
Now it should be kept ...
3
votes
1
answer
3k
views
Are dictionaries and associative arrays the same thing?
With respect to abstract datatypes (ADTs), are the terms "dictionary" and "associative array" perfect synonyms or are there slight differences between them?
- 167
3
votes
2
answers
521
views
Term for binary search tree using hashes?
I was looking for a way to easily store and access a symbol table using the least memory and code as possible and I went with a BST. Symbols, however, tend to be defined in order as in foo0, foo1, ...
user19863
8
votes
2
answers
4k
views
How are hash tables O(1) taking into account hashing speed?
Hash tables are said to be amortized $\Theta(1)$ using say simple chaining and doubling at a certain capacity.
However, this assumes the lengths of the elements are constant. Computing the hash of an ...
- 357
2
votes
2
answers
2k
views
Tree data structure for fast merges [closed]
I need trees that have the following properties:
Each node in the tree has two values associated with it - a key and an associated opaque data element.
An internal node in the tree has unbounded ...
- 23
2
votes
1
answer
260
views
Bloom filter variant
I've been playing around with a simple probabilistic data structure which is very similar to a Bloom filter. Where a Bloom filter would use $k$ independent hash functions to choose $k$ of the $m$ bits ...
- 222
31
votes
5
answers
3k
views
Is there an anti-Bloom filter?
A Bloom filter makes it possible to efficiently keep track of whether various values have already been encountered during processing. When there are many data items then a Bloom filter can result in ...
- 3,342
3
votes
2
answers
522
views
Why should leaf nodes in a red-black tree be black?
From the property of Red-Black Trees we know that:
All leaves (NIL) are black. (All leaves are same color as the root.)(Comren et al "Introduction to Algorithms")
But what is the reason that we ...
- 133
2
votes
1
answer
1k
views
What is a suitable data structure in this scenario?
I need an efficient data structure for maintaining a set of values.
Here, $n_1$ is the number of insertions per unit time; $n_2$ is the number of deletions per unit time; $k$ is the number of searches ...
- 221
9
votes
2
answers
2k
views
Looking for a set implementation with small memory footprint
I am looking for implementation of the set data type. That is, we have to
maintain a dynamic subset $S$ (of size $n$) from the universe $U = \{0, 1, 2, 3, \dots , u – 1\}$ of size $u$ with
operations ...
- 2,977
10
votes
3
answers
5k
views
Deleting in Bloom Filters
I know that standard Bloom Filters only have operations like inserting elements and checking if an element belongs to filter, but are also some modification of Bloom filters which enable a delete ...
- 219
3
votes
2
answers
2k
views
Data structure for maintaining large space-efficient filtered array
How does one implement a space efficient data structure that satisfies the requirements below?
You have a large array
You have a filter which tells you which elements in that large array are to be ...
- 155
4
votes
4
answers
504
views
Why do Bloom filters work?
Let's say I am using Bloom filters to create a function to check if a word exists in a document or not. If I pick a hash function to fill out a bit bucket for all words in my document. Then if for a ...
- 143