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Questions tagged [algorithms]

In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning.

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41 votes
2 answers
18k views

What is O(...) and how do I calculate it?

Help! I have a question where I need to analyze the Big-O of an algorithm or some code. I am unsure exactly what Big-O is or how it relates to Big-Theta or other means of analyzing an algorithm's ...
1654 votes
11 answers
837k views

Which hashing algorithm is best for uniqueness and speed?

Which hashing algorithm is best for uniqueness and speed? Example (good) uses include hash dictionaries. I know there are things like SHA-256 and such, but these algorithms are designed to be secure,...
Earlz's user avatar
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28 votes
7 answers
11k views

Should I keep investing into data structures and algorithms? [closed]

These days, I'm investing heavily in data structures and algorithms and trying to solve some programming puzzles. I'm trying to code and solve with Java and Clojure. Am I wasting my time? should I ...
Chiron's user avatar
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49 votes
8 answers
67k views

What methods are there to avoid a stack overflow in a recursive algorithm?

Question What are the possible ways to solve a stack overflow caused by an recursive algorithm? Example I'm trying to solve Project Euler problem 14 and decided to try it with a recursive algorithm....
Lernkurve's user avatar
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33 votes
6 answers
6k views

I'd like to write an "ultimate shuffle" algorithm to sort my mp3 collection

I'm looking for pseudocode suggestions for sorting my mp3 files in a way that avoids title and artist repetition. I listen to crooners - Frank Sinatra, Tony Bennett, Ella Fitzgerald etc. singing old ...
DeveloperDan's user avatar
3 votes
2 answers
301 views

What is the best algorithm for implementing a system with a complex execution path?

I am currently working on an implementation that based on a set of user configurations should output a final decision. The multiple configurations are evaluated several times at different stages of ...
MC.'s user avatar
  • 141
67 votes
17 answers
18k views

Is big-O really that relevant when working in industry?

In every interview I have been in, I have been quizzed on mathematical analysis of complexity, including big-O notation. How relevant is big-O analysis to development in industry? How often do you ...
21 votes
9 answers
8k views

How to turn truth table into smallest possible if / else block

How can I take a truth table and turn it into a compacted if block? For instance, let's say I have this truth table where A and B are conditions and x, y and z are possible actions: A B | x y z -----...
Juan's user avatar
  • 655
13 votes
7 answers
20k views

How important is studying algorithms and theory is to becoming a great programmer? [duplicate]

Possible Duplicate: Should I keep investing into data structures and algorithms? I'm a CS student. I want to become a really great programmer, what do I need to do to be come a great programmer? ...
Snow_Mac's user avatar
  • 349
9 votes
4 answers
11k views

Big-O for nested loop

I am reading this post on Big-O It says that the following code is O(n^2): bool ContainsDuplicates(String[] strings) { for(int i = 0; i < strings.Length; i++) { for(int j = 0; j &...
user10326's user avatar
  • 1,830
44 votes
14 answers
10k views

Unit-testing of inherently random/non-deterministic algorithms

My current project, succinctly, involves the creation of "constrainably-random events". I'm basically generating a schedule of inspections. Some of them are based on strict schedule constraints; you ...
KeithS's user avatar
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39 votes
2 answers
84k views

General way to convert a loop (while/for) to recursion or from a recursion to a loop?

This problem is mainly focusing on the algorithm, maybe something abstract and more academic. The example is offering a thought, I wanna a generic way, so example is only used as to make us more ...
xqMogvKW's user avatar
  • 543
22 votes
1 answer
42k views

What algorithm should I use to create an automatic staff scheduling feature?

Imagine a small local business (in my case a dog daycare) with a few dozen part-time employees . The goal is to automatically create weekly staff schedules. My question is about what algorithmic ...
Ghopper21's user avatar
  • 872
13 votes
3 answers
5k views

Please explain the statement that the function an+b belongs to O(n^2) and Θ(n)?

Let's say I have a linear function f(n)= an+b, what is the best way to prove that this function belongs to O(n2) and Θ(n)? I do not need mathematical rigor here. I need a programmers answer. Some ...
Geek's user avatar
  • 5,187
13 votes
6 answers
5k views

Is it inefficient to concatenate strings one at a time?

I recall back from my days of programming in C that when two strings are joined, the OS must allocate memory for the joined string, then the program can copy all the string text over to the new area ...
JSideris's user avatar
  • 601
10 votes
1 answer
2k views

Match two strings but allow for a degree of error

How can I match two strings, but at the same time allow for X number of characters to be incorrect in the match. The number of errors should be a controllable variable. While X number of characters ...
Reactgular's user avatar
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7 votes
3 answers
3k views

Algorithm for an exact solution to the Travelling Purchaser Problem

do you know of any algorithms which give an exact solution for the Traveling Purchaser Problem. I can only find heuristic and probabilistic approaches. I do have implemented a genetic algorithm so ...
scravy's user avatar
  • 387
5 votes
2 answers
3k views

Algorithm for mapping users to a schedule based on time availability

I have a project where I must map employees to a schedule. The basic concept is: Company Opens between 08:30 and 17:00. Employee 1 can work from 08:30 to 12:00 then from 13:00 to 1700; Employee 2 can ...
webnoob's user avatar
  • 2,159
1 vote
1 answer
2k views

How to test an algorithm with multiple inputs?

I want to check group of algorithms which has up to 8 input options. The native idea would be to check all possibilities via brute force. How can I reduce it without leaving out required combinations? ...
rekire's user avatar
  • 113
1 vote
1 answer
2k views

Unevenly distributed random number generation [duplicate]

Let's say I have to generate random number from 1 to 100, however, the probability of each number is not 1/100, but a predefined probability. How to generate that number? I use Ruby/Python.
Yoga's user avatar
  • 325
152 votes
13 answers
18k views

Is it just me or is this a baffling tech interview question? [closed]

Background I was just asked in a tech interview to write an algorithm to traverse an "object" (notice the quotes) where A is equal to B and B is equal to C and A is equal to C. That's it. ...
Matt Cashatt's user avatar
  • 3,315
143 votes
14 answers
14k views

Simple method for reliably detecting code in text?

GMail has this feature where it will warn you if you try to send an email that it thinks might have an attachment. Because GMail detected the string see the attached in the email, but no actual ...
62 votes
2 answers
42k views

Best practice/Patterns for two way data synchronisation

Quite often in my work the idea of 2-way data synchronisation between database systems crops up. The classic example is two slightly different CRM systems (say, Raiser's Edge and Salesforce) and the ...
codeulike's user avatar
  • 809
59 votes
5 answers
55k views

get weighted random item

I have, for example, this table +-----------------+ | fruit | weight | +-----------------+ | apple | 4 | | orange | 2 | | lemon | 1 | +-----------------+ I need to return a random ...
fl00r's user avatar
  • 701
52 votes
28 answers
119k views

What is your favorite whiteboard interview problem? [closed]

Just as the title says, what is your favorite whiteboard interview problem, and why has it proven effective for you? Junior, senior, Java, C, Javascript, PHP, SQL, pseudo-code, etc.
37 votes
7 answers
48k views

What algorithm would you best use for string similarity?

I am designing a plugin to uniquely identify content on various web pages, based on addresses. So I may have one address which looks like: 1 someawesome street, anytown, F100 211 later I may find ...
Squiggs.'s user avatar
  • 511
34 votes
6 answers
38k views

How do you identify "edge" cases on algorithms?

Basically how do you find out which could be your worst or best case and any other "edge" cases you might have BEFORE having them and so, how do you prepare your code for them?
Luis Armando's user avatar
31 votes
4 answers
6k views

Can you use Pi as a crude random number generator?

I recently saw this question over at math.SE. It got me thinking. Could Pi be used as a crude random number generator? I mean the results are well known(how long has pi been computed to now?) but, Pi ...
Earlz's user avatar
  • 22.9k
29 votes
4 answers
16k views

How to implement a Weighted shuffle

I recently wrote some code that I thought very inefficient, but since it included only a few values, I accepted it. However, I'm still interested at a better algorithm for the following: A list of X ...
Nathan Merrill's user avatar
27 votes
3 answers
17k views

Conflict resolution for two-way sync

How do you manage two-way synchronization between a 'main' database server and many 'secondary' servers, in particular conflict resolution, assuming a connection is not always available? For example, ...
K.Steff's user avatar
  • 4,505
22 votes
6 answers
2k views

When to prefer a generalized solution over solving specific cases

In programming we're often faced with a choice: cover each conceivable use case individually, or solve the general problem: Its obvious that solving the immediate problem is faster, however creating ...
AncientSwordRage's user avatar
22 votes
9 answers
18k views

Is it essential to learn algorithms to be a real programmer? [closed]

I'm a PHP programmer, and until now I have not needed to learn algorithms... Now I'm start learning Python (a real programming language), because I need to use matplotlib. Does it make sense to start ...
André's user avatar
  • 333
18 votes
2 answers
1k views

What class of problem is this, and what math do I need to know to solve it?

Mushroom cultivation requires fairly precise chemical composition of substrate (a.k.a. growing medium). Let's pretend we're growing shitakes and that this is the required composition of their ...
canisrufus's user avatar
  • 1,091
18 votes
5 answers
11k views

Algorithm for flattening overlapping ranges

I am looking for a nice way of flattening (splitting) a list of potentially-overlapping numeric ranges. The problem is very similar to that of this question: Fastest way to split overlapping date ...
Jollywatt's user avatar
  • 321
16 votes
5 answers
4k views

Algorithm for Learning development [closed]

This is a fairly general question. I know a bit of Perl and Python and I am looking to learn programming in more depth so that once I get the hang of it I can start developing applications and then ...
user9057's user avatar
  • 179
14 votes
2 answers
6k views

Amortized Analysis? (Worst-case Performance Guarantees)

What is Amortized Analysis? And how can it help me achieve worst-case performance guarantees in my programs? I was reading that the following techniques can help the programmer achieve Worst-case ...
Anthony's user avatar
  • 900
10 votes
2 answers
7k views

Name of the Countdown Numbers round problem - and algorithmic solutions?

For the non-Brits in the audience, there's a segment of a daytime game-show where contestants have a set of 6 numbers and a randomly generated target number. They have to reach the target number using ...
Dai's user avatar
  • 680
9 votes
1 answer
8k views

How are queues made thread-safe in Python

I admit this was asked to me in interview a long time ago, but I never bothered to check it. The question was simple, how does Python make Queue thread-safe? My answer was, because of Interpreter ...
Harsh Gupta's user avatar
9 votes
3 answers
12k views

Need help identifying a league scheduling algorithm

I am trying to create a sports league scheduler. I am having trouble identifying an algorithm to help me efficiently fill in each slot. Sample data to build the schedule would be: 10 teams Each ...
steve's user avatar
  • 191
6 votes
3 answers
1k views

Is it ethical to adopt other programmer's algorithms?

Imagine I find a completely new algorithm to compute the square root of a binary number (simplification of real scenario) on an internet forum that was an original creation. Is it ethical for me to ...
Drew's user avatar
  • 191
6 votes
3 answers
11k views

Why is the "period of a (pseudo)random number generator" important?

I've been trying to understand (pseudo)random number generator code from various sources and the concept of the period continues to elude me. To satisfy the minimum level of understanding, I've tried ...
Rich Wermske's user avatar
5 votes
3 answers
1k views

Fuzzy algorithm for grouping data

I have data that indicates which topics each student has got right/wrong in an assessment.: | Student | Topic 1 | Topic 2 | Topic 3 | Topic 4 | Topic 5 | ... (perhaps 30 topics) | 1 | T | ...
James's user avatar
  • 345
5 votes
4 answers
2k views

Search algorithm with co-ordinate (x,y) hints?

I am about to start writing a UI view where many small text items are laid-out over the view and when the user hovers over a text item a dynamically-generated image is displayed (like a tooltip), ...
trojanfoe's user avatar
  • 205
5 votes
3 answers
6k views

Algorithm to figure out appointment times?

I have a weird situation where a client would like a script that automatically sets up thousands of appointments over several days. The tricky part is the appointments are for a variety of US time ...
Rachel's user avatar
  • 24k
3 votes
4 answers
8k views

How to efficiently search a set of vectors for a vector which is the closest match

Unfortunately, I am not even sure of the keywords to use for this question, so if this has already been asked please point me the right way. Given a set of vectors: [3, 5, 3] [10, 23, 5] [123, 53, ...
Dan Gravell's user avatar
3 votes
4 answers
2k views

Fastest algorithm of dividing array into positive and negative numbers

Given array of integers I am trying to design the fastest algorithm that swaps the elements such that at the end : all negative elements are on the left and then the positive elements, for example, ...
user271261's user avatar
1 vote
3 answers
1k views

How to convert this recursive problem to iterative? Line Simplification algorithm fails to run due to Maximum Recursion Depth being hit

I am implementing the Douglas, Peucker's Line Simplification algorithm in Python. I started with this implementation. However, it fails to run in Python due to Maximum Recursion Depth being hit. How ...
skjoshi's user avatar
  • 113
1 vote
1 answer
496 views

Algorithm to find the fewest number of values (from a set of values) where the sum equals a value (+ one more condition)

The simplest way to explain this is with an example. You're given then number 19 and you have a set of numbers to choose from: 1, 2, 3, 4, 6 When choosing values from the list (which can be ...
Michael Waterfall's user avatar
0 votes
3 answers
514 views

How to Simulate Control-Flow without using Control-Flow Primitives

Basically, I want to know how to simulate while and if if I'm handling the control flow myself through an array of instructions. The while loop can be simulated by if, as seen with assembly branching ...
Lance's user avatar
  • 2,605
48 votes
6 answers
70k views

Can an algorithm be patented? [closed]

So can an algorithm be patented? I saw this statement which made me think: Everybody would abstain from patenting the improvements of contour dot algorithm for at least several years, say up ...
Shawn Mclean's user avatar