Questions tagged [algorithm-analysis]
Analyzing an algorithm to determine its time and space performance.
112 questions
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How to choose between brute force and efficient solution that has overhead?
Using Big O notation, it is clear that I should go with the more efficient approach, but I know that there is a significant cost in terms of initialization for more efficient solutions.
The Problem:
...
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3
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What is beyond ordinary c++, when trying to optimize a function?
Backstory:
Writing a QImage to Sixel renderer.
Feel like I have optimized it the best I can using basic c++.
I have heard suggestions here or there that you can utilize things like GPU, SIMD, insert ...
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3
answers
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Trying to understand the 2N lnN compares for quicksort
I was going through the analysis of quicksort in Sedgewick's Algorithms book. He creates the following recurrence relation for number of compares in quicksort while sorting an array of N distinct ...
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4
answers
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Check distance between all elements in a list of numbers in O(n*lg(n))
I have an exercise for my algorithms and data structures class, where I basically have to implement a divide and conquer algorithm or function called check_distance to determine whether all numbers in ...
- 101
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7
answers
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Why is big O notation an asymptotic notation/analysis?
An asymptote in mathematics represents a value (line) to which the observed function constantly approaches. In other words, as the value of X increases towards infinity, i.e. decreases towards minus ...
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Algorithms: How do I sum O(n) and O(mlog(n)) together?
I'm doing a running time analysis using the aggregate method and I'm a bit confused about what would be the result in this case. I have some intuition in inferring that it would be O(mlog(n)) but I'm ...
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Calculating time complexity of a code snippet
I am trying to calculate the time complexity of the below code snippet
def func()
{
for(i=1; i<=n; i++)
{
for(j=1; j<=n; j=j+i)
{
print("hello")
}
}...
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1
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1
answer
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Some questions about shortest-path algorithms
I'm trying to understand why anyone would prefer Floyd-Warshal over Dijkstra:
Dijkstra gives a correct result, using an understandable system, combined with backtracking.
Floyd-Warshal makes an ...
- 221k
1
vote
3
answers
239
views
How can I mix this grid to guarantee it being solvable in X minimum steps?
Note: This question is not about this particular instance of this grid with these exact words, but about any combination of words.
I am programming a puzzle game where you have to arrange a grid of ...
- 120k
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2
answers
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fastest way to find number of smaller elements to the right of an array
In Daily Coding Problem, Miller&Wu have the following problem :
Given an array of integers, return a new array where each element in the new array is number of smaller elements to the right of ...
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1
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What is the most suitable data structure for IPv4 addresses with intersecting ranges?
Mostly in all routers and operating systems the Longest Prefix Match algorithm is used for searching the trie of IPv4 addresses.
Packet filters like Iptables don't need some special data structure for ...
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1
answer
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Counting primitive operations on recursive functions
I'm reading Algorithm Design and Applications, by Michael T. Goodrich and Roberto Tamassia, published by Wiley. They teach the concept of primitive operations and how to count then in a given ...
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vote
2
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More efficient alternative that checks if a list can be made a palindrome
For my algorithms and data structures class, I have to write an algorithm that is more efficient in the worst case than the following algorithm:
def algo_X(A):
i = 0
j = len(A)-1
while i &...
- 182
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votes
4
answers
685
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Processing a 2D matrix - need to speed up my O(n^4) algorithm
I have an n x n matrix which I need to convert into a list sorted by value. Starting with the maximum value cell at (row x1, col y1), I must immediately exclude all cells where (x >= x1, y <= y1)...
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1
vote
2
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Does a microcontroller provide better accuracy for comparing algorithms' run-times?
I have a set of algorithms to choose from based on their execution speed. I know that it is very hard to get an accurate measurement due to the process scheduling, the time that is actually consumed ...
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3
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1
answer
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Why the names Omega and Theta in Big Omega and Big Theta?
There was a question asking what the "O" stands for in "Big O", the answer to which seems to be "Ordnung von"/"order of".
I wonder what's the origin of the ...
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1
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Running time for simple for loops - Big O notation
I am currently doing some exercises with algorithms and I find myself in a huge problem.
It seems that everybody understands this type of problem but I have a really hard time figuring it out. For ...
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2
votes
2
answers
257
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Time complexity for a small code
I'm trying to find the time complexity for the following code.
N= number of elements in array
D= a constant: D>1
V= a constant: V>1000
counter=1; //the maximum value of the counter is N/D.
...
CommunityBot
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votes
6
answers
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Using a different algorithm depending on the size of the input
I recently finished a course on advanced algorithms, and another on complexity & computability theory, and in the past few days my mind has been somewhat preoccupied by this question.
Why don't we ...
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4
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2
answers
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How can I know when a paper is too hard for me to be able to implement their code and/or understand their math - within a given deadline?
I've been assigned to explore implementing (along with modifications, so understanding it is a must) this algorithm for the 'Redistricting Problem': https://dl.acm.org/doi/pdf/10.1145/3274895.3274979 ....
- 149k
1
vote
0
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Rectangle packing / Bin packing with multiple frames
I have multiple rectangular frames, with different fixed heights. The width should be minimized and there is a maximum width. Then there are many different smaller rectangles. These should be packed ...
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3
answers
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Are there any programs or IDEs that calculate Big-O notation on functions? Is this something that is possible to program into an IDE?
Is there anything that can calculate the Big-O notation of a function?
While learning about Big-O, it is implied that it is pretty trivial to do in your head once you know the basic rules, however if ...
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votes
3
answers
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Is O(log n) + O(log n) = O(n)? [duplicate]
We know that binary search takes O(log n) in Big O notation but if we need to run twice an algorithm of O(log n), would it be the same as O(n) in time complexity?
For example, if I have a method to ...
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1
answer
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Time complexity of a Nested While loop in a for loop
I'm trying to derive the simplified asymptotic running time in Theta() notation for the two nested loops below.
For i <-- 1 to n do
j <-- 1
while j*j <= i
j = j+1
For i <-...
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0
votes
1
answer
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Do I have do use HashTables/Maps/Hashmaps in this algorithm?
I am doing the Ransom Note algorithm in Hackerrank. The thing is I am not using maps and all the tests pass except for three which execution time takes a lot more. (Kotlin language)
I have two ...
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2
votes
1
answer
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Do we include output space in space complexity?
For example. I have a function which generates an array with random numbers.
int[] generateNum(int n) {
int[] result = new int[n];
/* Logic to generate random number */
...............
...
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-1
votes
1
answer
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views
static, dynamic analysis - what mistakes were made in the code?
A software company develops software packages for commercial animal
farming. A special function in C calculates the daily amount of feed
for different kind of animals dependent on their bodyweight....
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5
answers
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How to discriminate from two nodes with identical frequencies in a Huffman's tree?
Still on my quest to compress/decompress files with a Java implementation of Huffman's coding (http://en.wikipedia.org/wiki/Huffman_coding) for a school assignment.
From the Wikipedia page, I quote:
...
3
votes
6
answers
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views
Is it better to write an efficient algorithm or code that is easier to understand?
So I was recently given a coding assignment from a large financial firm, and I thought of two ways to solve the problem. One of the ways involved 1 outer for loop and 1 inner for loop. In this case, ...
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1
vote
0
answers
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Logfile correlation finder (for j4Log)
I'm currently analyzing a problem in a old "distributed" system, that only occurs sporadically - as the system does not support other means of debugging help I have to rely on the logs (I did not ...
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Questions around calculation of time complexity of an algorithm [duplicate]
I am a newbie to algorithms. One thing that i always get confused is about calculation of algorithm runtimes.
For example: The following piece of code in Python
for i in range(n):
#O(?)
i*=k
...
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1
answer
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views
Battery level prediction model
I have the idea of develop a model that predicts the battery charge level of my system for now until the following 5 days. The battery is charged using a solar panel. I am writing my code in Python 2....
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1
vote
1
answer
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views
How to reason about complexity of Merging k sorted linked lists?
I am trying to understand Big O notation better to be able to reason about it in a much clearer way and therefore, need some feedback on my analysis given below for problem: Merge k-sorted linked ...
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1
answer
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Algorithm: Binary Search / Tree / Partitioning on unsortable data?
First, this question is not really about binary search as I neither have sorted data, nor any sortable data at all. :-)
W.r.t the "unsortable" claim see below; but I think the title term "unsortable"...
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4
votes
1
answer
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Sublinear Extra Space MergeSort
I am reviewing basic algorithms from a book called Algorithms by Robert Sedgewick, and I came across a problem in MergeSort that I am, sad to say, having difficulty solving. The problem is below:
...
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vote
1
answer
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Why is the optimal choice for a pivot in quicksort algorithm the median element?
Lately i have been taking an course at brilliant.org, i was exploring a lesson on QuickSort algorithm, found a question.
Which of the following would provide the optimal pivot selection at each step ...
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1
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Is my reasoning to determine this algorithm's Big-O correct?
Take the following algorithm with two separate sections, and the sections do not influence each other whatsoever (the function is not recursive, as well).
void algorithm(int x)
{
// This section ...
1
vote
1
answer
2k
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Reverse engineering a checksum or CRC
I am trying to reverse engineer a checksum or CRC wherein an 8 bit number* gets converted to a 5 bit number for error checking. I have an incomplete list of data values and checksums, and need to ...
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1
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Help with algorithmic complexity in custom merge sort implementation
I've got an implementation of the merge sort in C++ using a custom doubly linked list. I'm coming up with a big O complexity of n^2, based on the merge_sort() > slice operation. But, from what I've ...
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4
answers
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How does the dividing Step in Merge Sort have Constant Time Complexity?
I am highly confuse while calculating time complexity of Merge Sort Algorithm.
Specifically on the Dividing Step.
In the dividing step we have to calculate the mid point of "n" i.e. "q = n/2".
How ...
6
votes
3
answers
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Effecient algorithm for data deduplication in procedural code
I have written a data cleansing application which, for the most part, works well. It is not designed to handle large volumes of data: nothing more than about half a million rows. So early on in the ...
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votes
0
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String Pattern Matching from Lookup Table - Non-Exponential Solution?
Given the problem...
Given a String comprising of non-alhpabetical symbols, and a Lookup
Table where a subset of those symbols may equate to a single
alphabetical character, output all possible ...
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3
votes
2
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Estimating run time of algorithm
For instance if i have an algorithm that is O(n2) and it will run for 10 seconds for a problem size of 1000. Now if i were to double the problem size to 2000 i want to know the approximate run time in ...
5
votes
1
answer
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A* Algorithm Completeness Proof
The A* Algorithm is the optimal (provided the heuristic function is underestimated), complete & admissible (provided some conditions). I know the proofs of admissibility & optimality.
But how ...
- 221k
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votes
8
answers
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Why is binary search,which needs sorted data, considered better than linear search?
I have always heard that linear search is a naive approach and binary search is better than it in performance due to better asymptotic complexity. But I never understood why is it better than linear ...
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vote
1
answer
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Sorting method for music avoiding title and artist repetition
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 ...
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Why in Tournament Sorting do we neglect the number of comparisons to find the Minimum?
Here the professor said that, Tournament sort needs (n-1) + 2(n-1)logn comparisons.
{Where (n-1) for calculating Maximum or say creating Tournament structure
and
2(n-1)logn for other elements to sort}...
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votes
7
answers
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What is wrong with this algorithmic solution of mine that checks whether a given function returns a sorted array when an array is given as input?
An interviewer asked me this question:
Given a function f(ar[]) where ar[] is an array of integers, this
functions claims to sort ar[] and returns it's sorted version ars[].
Determine if this ...
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vote
2
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Loop invariant of Selection Sort
Selection Sort(A[1,2..n]:array of integers)
1.for i=1 to n-1
2.for j=i+1 to n
3.if A[j]<A[i]
4 swap(A[i],A[j])
I am trying to prove the correctness of this algorithm,I read from my book ...
CommunityBot
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1
answer
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Calculating Complexity
I am having trouble calculating the complexity of this problem:
REVERSE3(A): // Reverse the order of elements in an array
// P is an array; assume generating next permutation takes 1 step.
for ...
CommunityBot
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