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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Multi-pattern matching

I have a given byte array in C and I need to match it against several byte arrays and return true if there is any match. I can make various memcmp's but I feel that it is very inefficient. Do you ...
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2answers
580 views

Is the time complexity of a while loop with three pointers different than 3 nested for loops?

This program (written in ruby) finds the largest 3 numbers in an array (without sorting the array). It has a while loop with three pointers. My fist instinct, since there is only one loop is to say ...
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4answers
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When speaking, how can I say that the time complexity order of an algorithm is O(N log N)?

What term can I use to describe something with O(N log N) complexity? For example: O(1): Constant O(log N): Logarithmic O(N): Linear O(N log N): ?????? O(N2): Quadratic O(N3): Cubic
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1answer
306 views

Precedence of function in Shunting-yard algorithm

I am working through the Shunting-yard algorithm, as described by wikipedia. The description of the algorithm when dealing with operators is as follows: If the token is an operator, o1, then: ...
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0answers
61 views

clustering of strings with variable-length prefixes

I've got bunch of strings with variable-length prefixes (or postfixes - I can always revert them) as follows: 0155555555 523455555555 755555555 ... 87129999999999999 119999999999999 09119999999999999 ...
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1answer
65 views

Looking for an Appropriate Search Algorithm

I am currently planning an upcoming project and am looking for an algorithm for searching a database. The search is as follows; There will be some specifically labelled criteria (or fields) and I ...
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1answer
211 views

How to generate Generate Hash incorporating time stamp so it can be unhashed to get the timestamp when it was generated?

I want to create hash based on random id, That hash has to be valid for only 15 minutes. Is there a way to do that? I'm using this for form submission. If some unknown submitted form or some one ...
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1answer
199 views

Finding the optimal root

I am trying to solve a quora hackathon challenge question. The question descrpition is as follows : For the purposes of this problem, suppose Quora has N questions, and question i (1≤i≤N) takes ...
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0answers
320 views

Fast fixed-size (256 bit) integer modulo/division

What is the fastest way to divide two 256-bit integers? They are represented as an array of 26-bit words, each stored in 32-bit integers. I have access to a 64-bit type if that's useful. It seems ...
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2answers
108 views

Why use a unique hashkey for form submissions?

I have multiple forms and use AJAX to submit them. I asked my boss if he needed any specific format for the form ID and he told me to generate a unique hash and keep it in session; check it whenever ...
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2answers
129 views

Integer Map Algorithm [closed]

For my project, I need to map integers so that inputting int X will output int Y where both X and Y are defined during runtime. I've used Dictionary<int,int> in .NET but its memory use is too ...
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1answer
196 views

How to sort fractions (small numbers)

We have 100 000 fractions: Let's consider following fractions. p/(2^q) such that 0 <= p,q <= 10 As you can see there are <= 10 * 10 different fractions, but we have 100 000 that we have to ...
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1answer
136 views

Algorithm to cut out and straighten rectangles from image

I am looking to write an algorithm to cut rectangular images and straighten them in a new image. The bigger concept is that I will be scanning a bunch of physical pictures (on a physical scanner). ...
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2answers
106 views

AABB collision algorithm with a condition

So I'm doing a 3D implementation of collision detection. Considering Boxes are oriented on the axis. They are rotatable but has to be orientated on the axis. Box A and Box B cannot go through each ...
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1answer
78 views

Seeds distribution algorithm with complexity better than O(n^3)?

I have included my approach and solution. My solution works fine, however, is unoptimized with O(n^3) complexity An NGO is running seed distribution program. It has limited quantity of varied quality ...
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2answers
165 views

Algorithm to solve this “treefarm” puzzle

How would I go about writing a program to solve this kind of puzzle: The green squares represent trees, and you have to plant them in such a way, so that: Trees do not touch each other at all (not ...
3
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2answers
188 views

Obstacle bypass in 2d environment

For this 2d grid (black square are not penetrable, white square are): I want to find path who permit to move an object to a start point (x:18, y:18) to a end point (x:1, y:1), square by square. ...
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2answers
178 views

Work out which parcel deliveries we ship ourselves and which we outsource

Firstly, I hope I'm asking this in the right place. I work for a large online retailer in UK. We ship approaching 2000 orders each day and are growing very quickly. We currently use multiple delivery ...
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5answers
275 views

Hamming Distance using a dictionary

First time poster. I'm currently programming a hamming distance program using a dictionary. So if we start with the word "cat" and we want to transform it into "dog", the sequence is ...
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0answers
51 views

Final array after M updates on Segment Tree

I am stuck in a middle of a problem. I have made segment Tree of N elements and performed M updates through lazy propagation Now I need to store the final array (to some array B of size N) after all ...
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1answer
163 views

What does it mean for an algorithm to converge?

I keep coming across this term when reading about reinforcement learning, for example in this sentence: If the problem is modelled with care, some Reinforcement Learning algorithms can converge to ...
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1answer
59 views

Which algorithm to find the shortest (nodes count) path that encompasses all polygons inside a larger polygon?

Inside a large polygon (say the USA boundaries) I need to find the shortest path that will encompass smaller polygons (say the following cities: Kansas city, St Louis, Memphis, Oklahoma City) By ...
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1answer
118 views

Improve bisection method or alternate algorithm for efficient determination of text font size to fit in a box

I need to find the font size of a text that fits in a box. Given my current font size, I can get the bounding rectangle of the text. If I set some arbitrary min and max font size, I suppose I can ...
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0answers
127 views

Software Design, Generic Programming, Physical Devices, and Algorithms in C++ [closed]

I often have data that in some contexts I want to handle uniformly, but in other contexts I wish to differentiate it. For example, I could have a vector that is series of angles or a series of ...
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0answers
41 views

Approaches to combinatorial optimization problem

Problem I have the following combinatorial optimization problem: A set of applications need to be distributed among a set of nodes. Each node has a capacity and each application has a required ...
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67 views

Simple Path to Route Algorithm

I'm currently conducting research into subway paths, but stand in front of a problem, with no programming knowledge and an extremely short time-limit. Probably the question I am asking is trivial, ...
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2answers
205 views

Algorithm and data structure to match groups of users (1-5 each) into 2 balanced sets of 5 users

I'm building a matchmaking queueing service for a 5v5 team-based game. I have a large set of users that are grouped into unique lobbies comprised of 1-5 users each. Each user has an integer based ...
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1answer
205 views

Minimizing compression overhead in a simple compression algorithm

Note: this question has been re-written to simplify and generalize the problem. The original is available below. Suppose I created a simple compression scheme for lists of 2-digit numbers. It has 2 ...
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2answers
101 views

(Partially) Sorting a lazy-evaluated collection

So I'm trying to implement a lazy-evaluating data type (in PHP, though that shouldn't matter any) where you can queue up actions to take on a set of data. This data can come (theoretically) from any ...
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1answer
136 views

Is external merge sort a divide-and-conquer algorithm? [closed]

Today I was corrected for mentioning "External Merge Sort" as an example of a divide-and-conquer (D&C) algorithm and after doing a lot of research online and in the most prominent books on ...
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84 views

Efficient extensions of degree of separation

I'm trying to play around with the 6 degrees of separation problem, specifically the Kevin Bacon game to find alternative ways of playing the game. I want to eventually port it over to MapReduce, but ...
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5answers
2k views

Simple and clean way of comparing three numbers

I've got some code that has a sequence of ifs that work, but just feel messy. Basically, I want to choose the largest of three integers and set a status flag to say which was chosen. My current code ...
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5answers
648 views

Drawing concentric circles without gaps

I want to fill a circle with alternate colors like a lollipop by drawing circumferences of increasing radius on a Cell matrix. I am currently using the Midpoint circle algorithm to get the points. The ...
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2answers
217 views

Algorithm to find the optimal trade route (negative cycle with lowest cost per edge in a digraph)

Given the following problem (a slightly simplified description of trading in the computer game Escape Velocity: Nova (system map)): Given a set of (solar) systems. Each system is connected by ...
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2answers
275 views

Find the maximum number of pairs of numbers that are in a range, between two arrays

Lets say I have two arrays A and B A = {1,2,3} B = {12,11,67} and have max sum value S = 10 How many maximum number of unique pairs can be formed between the two arrays who's sum is less than or ...
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4answers
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Are Constant Time and Amortized Constant Time effectively considered equivalent?

I need to write a RandomQueue that allows for appends and random removal in Constant Time ( O(1) ). My first thought was to back it with some kind of Array (I chose an ArrayList), since arrays have ...
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2answers
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What does pi mean in this BFS algorithm pseudocode?

I have the following pseudocode for breadth-first search algorithm BFS(G,s) 1 for each vertex u ∈ V(G) \ {s} 2 color[u] = white 3 d[u] = ∞ 4 π[u] = nil 5 color[s] = gray 6 d[s] = 0 ...
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0answers
82 views

Choose a number of arrays which have the smallest cardinal number when unified

Say we have multiple arrays: var a := [1, 2, 3] var b := [2, 3, 4, 5] var c := [1, 3, 4, 6] var d := [1, 2, 5] We want to find the three arrays with the smallest cardinal number when the three ...
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1answer
325 views

Fast indexing of k-combinations

I'm revisiting an old problem that I was working on some time ago. A typical scenario is "3 bits are set within an 8 bit integer", i.e. 00000111. All unique combinations with 3 set bits can easily ...
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2answers
123 views

Shape-Checking algorithm

I normally have a very intuitive approach to an efficient algorithm. In essence, I know what the bottleneck is, and how I can improve the algorithm. However, I'm now stuck and I am in the need of some ...
2
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3answers
71 views

Find all circles that cover one point

I'm not sure if I've been searching using the wrong keywords, but I've tried so many different ways of wording this and I can't find a relevant answer. Basically, given a set of circles defined by ...
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1answer
491 views

Algorithm/data structure to answer “what recipes can I make with this set of ingredients?”

Formally, let s(U, Q) = {V | V ∈ U and V ⊆ Q} where U, Q, and V all represent sets, and U, more specifically, represents a set of sets. For the sake of example, U might be a set of the (sets of) ...
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1answer
60 views

Need semi-efficient algorithm for 3-dimensional increasing sequence

I have a set of puzzle challenges for a prototype jigsaw puzzle kit, similar to commercial products offered by Thinkfun and Popular Playthings. I have a candidate list of 300 puzzle challenges and ...
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1answer
212 views

Algorithm to compute k-permutation without repeating and no duplicates

I have a set of integers, for example 1..20 and I want to get all possible combinations of that set drawing 5 numbers. So each combination has 5 numbers from that set of integers. But I don't want ...
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2answers
85 views

Given an array of n bits, how to generate every permutation with i 1's and n-i 0's?

It's simple enough to brute force a collection of strings and then filter for every occurrence with the required count of 1's. As n increases the number of possible permutations becomes very large, ...
3
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1answer
170 views

Best-matching comparative values using all items in array

I have two arrays of objects (items) in the exact same format. Each item represents a wager, and each array represents one of two outcomes for that wager (ex: Team A vs Team B). Both arrays look ...
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3answers
160 views

Find a line that is closest to scattered points

I came across the below interview question on Glassdoor: A scatter graph of points on a page, draw a horizontal line across the page such the the perpendicular y distance to the line from all ...
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0answers
115 views

Reversing dithering algorithms?

I was trying to make an implementation of the Floyd-Steinberg dithering algorithm in Python, and I was wondering, since Bitmaps files store their data starting from the bottom-left corner, would it be ...
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5answers
4k views

Advantage in being the first to copyleft a new algorithm? [closed]

Say I have created a new (DSP) algorithm. Will I have some advantage if I open source the algorithm under copyleft licence (GPL etc.)? From what I know about licensing this should lock people out from ...
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0answers
47 views

Project a piece of image cut by N-vertex shape to a different N-vertex shape

I have an N-vertex shape that I cut out from an image, and I want to project it onto another shape with the same amount of vertices, but different. So, the image will get changed inside the ...