Questions tagged [algorithm-design]

Questions related to general, high level, techniques for the design of algorithms.

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Finding the k-th baseball card purchased in an array of tuples with year and number of baseballs purchased in that year in O(n) time

Edit: Problem has been solved! Thank you @orlp and only you for actually taking the time to be helpful and giving me the hint that got me to progress!
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29 views

Intersection of line segments induced by point sets from fixed geometry

I am reading up on algorithms and at the moment looking at the below problem from Jeff Erickson's book Algorithms. I solved (a) by seeing a relationship to the previous problem on computing the ...
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1answer
44 views

Partition the indices of 2d array to minimize sum of sub-matrices

Given an $n\times n$ Matrix $M$, and the indices $[{1,2,3,4,...,n}]$ are divided into several intervals : $[1,x_1],[x_1,x_2],...[x_k,n]$, which further extract several squared sub-matrices along the $...
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1answer
34 views

Multi-Path Length Minimization

I've been thinking about path planning and am trying to make good heuristics for cases with multiple agents. Suppose there are sets $S_i$ of coordinates in $\mathbb R^2$ or $\mathbb R^3$, each of the ...
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1answer
77 views

“Searching and sorting” algorithm to find the natural logarithim of a number?

Yeah, this is for a homework assignment, but I hope that you'll humor me anyway. I am asked to design an algorithm that finds the natural logarithm of a number. This would be straightforward, but I'm ...
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1answer
87 views

Mutli-Path Collision Avoidance

I need an algorithm which can do the following: Given some finite number of particles (circles) each with the same radius, and a list of prescribed points for each particle, find paths in $\mathbb{...
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1answer
52 views

Finding lost bottle (algorithm problem)

The question is as follows: A scientist creates a new compound, called compound A, that will explode 10 days after being mixed with compound B. This compound A was stored in a label-less bottle on ...
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1answer
47 views

Maximum number of similar groups of a given size that can be made from a given array

I am given an array of numbers, not necessarily unique, and the size of a group. Let the array be denoted by $B$ and the size of the group be $A$. I need to find the maximum number of groups with the ...
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59 views

Doubt on integrality gap and LP relaxation

I have an exercise that tells me that, given a problem P (of which now I omit the description) there is no integrality gap between LP and ILP formulation of this problem, and for every fractional LP-...
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1answer
26 views

Is it possible to estimate the step size and walking velocity of different person with the x-y-z acceleration data from 6 axial accelerometer sensor?

I have a 6-axial sensing device used to record the acceleration data. There is an algorithm used to count the number of step and walking distance of the user, but I want to further increase the ...
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17 views

How to divide services and capacities in a graph?

Given a graph where some nodes can provide some services with x,y,z... capacities. A node connected to multiple nodes needs to divide these services to the connected nodes and these nodes themselves ...
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1answer
40 views

design cache system using queuing theory

If we have data from a random population, a 3d histogram of throughput and current cache size of DRAM (intersection of a IOPS & a cache size will have a count). How can one use queuing theory to ...
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1answer
80 views

Given an array of size n, create a sub array with given conditions using dynamic programming

We are given an array of integers of size n, which is not necessarily sorted, and we want to create a sub array. We are allowed to do one of 3 tasks below in each level: 1. skip the number in original ...
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2answers
56 views

Lexicographic permutation list

Does anyone have an algorithm for stepping through all permutations of n given arbitrary objects in lexicographic order? Thanks.
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1answer
161 views

Can a greedy algorithm have more than one subproblems to solve after making greedy choice?

For example: s = <s1 s2 s3> is my problem, I make greedy choice s2 and solve s1 and <...
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1answer
339 views

Greedy algorithm for even item distribution

I have this problem where I need to design a greedy algorithm. The problem is as follows: A chocolate factory owns $n$ stores, which are connected by a single road. Each store has a limited supply $...
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1answer
31 views

Finding max value algorithm with subset comparison

I have a set of $N$ different values, and my goal is to find the biggest one in the least number of comparisons. Comparing subsets (using the sum of each) is also allowed, and counts as one comparison....
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1answer
6k views

Implementation of QuickSort to handle duplicates

I have this past year question based on the following scenario: When the list of items to be sorted contains a lot of duplicate values, we can improve QuickSort by grouping all the values that are ...
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1answer
206 views

Longest substrings of common length with the same parity

Given two sequences $a$ and $b$, find largest $x$ such that in $a$ there is substring $A$ and substring $B$ in $b$ meeting those conditions: length of both $A$ and $B$ is equal to $x$; sum of ...
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1answer
236 views

Algorithm to organize a tournament where the team componentes change each round

So, I was tasked with creating an app that generates the schedule of a doubles tennis tournament (i.e., teams of two) in a way that, by the end of it, everyone would have played against the rest of ...
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36 views

Trouble Convincing Myself Algorithm Correctness

I'm having a tough time convincing myself right when coming up for some solutions to medium/hard leetcode.com problems. Take the following question for example. ...
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1answer
78 views

Avoiding correlated values and reduced collision resistance in multiple hash states

I need to design a hash function that fits this criteria: Limited to 32-bit integer operations (for compatibility with JavaScript bitwise operations, my target system) Produces an n-bit hash digest, ...
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72 views

Arrange objects in space so that the outline takes the least surface/volume

Imagine you have a number of 2-dimensional objects. The question is how to fit them all in a rectangular space in such a way that this rectangle takes the smallest area possible. On the below image ...
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1answer
63 views

Develop a winning strategy for a game

Okay so I've been going crazy about this problem I was given. It is as follows: Given a pile of N matches, 2 people take turns removing matches from the pile. When it is your turn you are allowed ...
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3answers
122 views

Finding one of 2/3 of all array elements in constant expected time

How do I go about designing a constant time algorithm which satisfies the following I/O requirements: Input: an array $A$ of length $3n$, containing $2n$ values of the symbol $X$ and $n$ of the ...
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1answer
83 views

How to create an algorithm when given the invariant

I am given the following invariant: Invariant The greatest $i$ keys of an Array are always in sorted order on the last $i$ indices of the Array. I am supposed to ...
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288 views

Non-deterministic Turing Machine recognizing a context-free Language

This question is taken from an exam of a Computer Theory Course. Describe how a NON-Deterministic Turing Machine with two tapes recognize the language generated from the grammar: $ S \rightarrow SS ...
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701 views

Deformation of algorithms

Has there been any attempt at a general theory to describe how an algorithm can be "deformed" to solve the problem more efficiently? For example suppose we have an algorithm (say sorting a list of ...
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216 views

Implementing supplies in Coin change problem

I started an algorithm course in C two months ago, for the last weeks I've been trying to solve this problem , i ran out of time but I cannot find an acceptable solution. Basically It's a coin change ...
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1answer
226 views

A general algorithm for greedy algorithms

I have been refreshing on greedy algorithms as an algorithm design technique. I have read many sources for an explanation of what a greedy algorithm is, because I would like to put together a general ...
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38 views

Is it correct to say that there are similarities between CORDIC and digit recurrence algorithm for division?

I've been studying recently some variations of the CORDIC, and it seems to me that the logic behind at least the basic cordic or the redundant CORDIC is very similar to the logic used to design digit ...
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1answer
52 views

4 Neurons to Decide 10 Digits

I am trying to solve this algorithm exercises (http://neuralnetworksanddeeplearning.com/chap1.html#exercise_513527) in Michael Nielson's online book: Neural Networks and Deep Learning (http://...
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1k views

How to Match Socks

When I do my laundry I tend to make a pile of unmatched socks, putting new socks on the top of the pile and matching off pairs if two of the same sock are near the top of the stack. Since eventually ...
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1answer
21 views

A comparison operation for lists, based on P(a > b)

Consider two lists $A$ and $B$, both containing $n$ numbers. A comparison operation can be defined based on the probability of uniformly selecting an element $a$ from list $A$ and an element $b$ from ...
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1answer
51 views

Counting permutations whose elements are not exactly their index ± 1

This is a special case of the question: Counting permutations whose elements are not exactly their index ± M The $M=0$ case has already been solved, but no one was sure how to work out the non-...
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3answers
621 views

Finding longest balanced parentheses using $n$ smaller strings

Given $n$ strings consisting only of '$($' and '$)$', how one can compute the length of the longest string that can be built by concatenating a subset of these strings in some order such that the ...
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2answers
245 views

Counting permutations whose elements are not exactly their index ± M

I was recently asked this problem in an algorithmic interview and failed to solve it. Given two values N and M, you have to count the number of permutations of length N (using numbers from 1 to N) ...
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1answer
138 views

improve the running time

How can I use divide and conquer to improve the running time of this algorithm? input: A sorted array of length n output: the # of elements such that abs(A[i]) <= k
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17 views

Without sound synthesis, what is a good way of making a program that plays guitar notes from an array of stored sounds?

Without sound synthesis, what is a good way of making a program that plays guitar notes from an array of stored sounds? What I have in mind is to make note as a function of vibration speed such as N (...
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3answers
98 views

Beginner help with Arrays & Complexity

My goal is to create a method that gets an array that only has 1's and 0's in it, and then turns every number into the amount of 'steps' it is away from the closest 0, left or right. So for example [...
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613 views

Designing bidirectional search algorithm

Write down the algorithm for bidirectional search, in pseudo-code. Assume that each search will be a breadth-first search, and that the forward and backward searches takes turns expanding a node at a ...
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1answer
633 views

Is there a formalization of a general version of the sweep line algorithm? If not is it easy to derive?

A well known algorithm in computational geometry is the sweep plane algorithm. I've been trying to find if there's a general version of the sweep plane algorithm in $\mathbb{R}^n$, I don't need to ...
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1answer
68 views

finding a & b in an array that a+b = x, for a given integer x [closed]

I want to get an algorithm with $\theta(nlogn)$ time complexity that search for two elements in an array of integers, which their sum is equal to $x$ such that x is an integer and $n$ is array size.
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1answer
157 views

Why does counting sort copy the input elements?

When I was reading about counting sort in Introduction to Algorithms for the first time, I stopped reading after the step where they calculate the number of each element in the input array. It's the ...
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2answers
822 views

Find all rational roots of a polynomial equation

I'm going to try to design an algorithm to find all the rational roots of a polynomial equation in range [a, b]. Can someone please tell me which algorithm currently solves the problem with lowest ...
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2answers
267 views

Any algorithm better that O(N*logN) for a problem of finding student with largest average score in a list of N scores of the form StudentID, score

Question: Suppose you are a given a csv with N lines of the form StudentID, score. Multiple lines can have same student-ID. Find the student with maximum average score I can't think of any way to ...
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2answers
655 views

Algorithm and proof for combining a list of node connections into groups of nodes efficiently

My goal is to algorithmically take a list of relations between nodes (in other words, a list of undirected edges between nodes of a graph) and label each group of nodes such that all nodes that have a ...
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3answers
124 views

Why is reduction mostly associated with proving hardness?

Reduction is a powerful problem solving technique that is helpful in solving problems in terms of the solution to other problems, it can also be used for complexity analysis. Why does most of the ...
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1answer
2k views

Is there Any difference between dynamic programming vs branch-bound vs delayed column generation

I was reading about cutting stock problem https://en.wikipedia.org/wiki/Cutting_stock_problem , this is best solved using dynamic programming but wiki page mentions 2 other techniques names Branch-...
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944 views

Josephus Problem - A faster Solution

I came through Josephus problem a little while ago. Problem is stated as follows : "People are standing in a circle waiting to be executed. Counting begins at a specified point in the circle and ...