Questions tagged [complexity]

Complexity is the analysis of how the time and space requirements of an algorithm vary according to the size of the input. Use this tag for reviews where the "Big O" is a concern.

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9
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1answer
1k views

Codility MaxCounters peformance in Python capping out at 77% performance

My problem is quite similar to the question found here, except I am attempting to answer the question in Python. Given an array of N counters, all initialized to 0, and an array ...
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4answers
7k views

PermCheck Codility with time complexity of O(N)

I have this solution for Codility's PermCheck problem. In summary, the task is to check whether array A contains each number in \$1 \ldots N\$ exactly once. I got ...
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1answer
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Permutations of any given numbers

I have solved one programming problem where we have to find all the permutations of given numbers. For example, \$[1,2,3]\$ have the following permutations: $$[1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,...
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Finding unique triplets adding up to 0

I am working on a problem "3Sum", in which, given an array S of n integers, are there elements ...
8
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1answer
97 views

Joining collections… because it's fun

I'm working on a LinqEnumerable class (reviewable here), and I'm no Big-O expert and I'm pretty bad with algorithms, so I wonder what the complexity is for what I'...
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1answer
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Finding the longest unique sub-string in a string

I recently interviewed with a company for software engineering position. I was asked the question of finding the longest unique sub-string in a string. My algorithms was as follows: Start from the ...
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2answers
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Re-arrange a string into a { consonant, vowel, consonant, vowel … } sequence

I was prompted to give someone advice about the following problem: Given a string with equal amount of vowels and consonants, re-arrange it so that it follows the sequence { consonant, vowel, ...
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3answers
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Print all nodes from root to leaves

I've made a function to print all paths from root to all leaves in a binary search tree. I already have an insert function, which I haven't included in the code here as I felt it was irrelevant to the ...
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2answers
365 views

Fastest way to find maximum deviation

I acknowledge that this exact question was asked here. I was working on the same problem from the same website. I had the same question and consulted the above as a reference, however with respect ...
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1answer
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Time complexity of anagram solution

I have written code to return anagrams from a list of words. I'm a newbie in time complexity analysis so pardon my ignorance if this is a blatantly obvious question. Am I right in thinking this is in ...
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2answers
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Finding the largest repeating substring

Here's my code that takes a large string, and searches for the longest reoccurring substring. It compares the first letter with every other until it finds a match, then saves it. Then it compares the ...
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1answer
167 views

Time complexity of 0/1 Knapsack challenge

The code gives correct output. How do I calculate time complexity for code like this? The program finds all the combinations of items and sees if the combination gives the max profit. If the last ...
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2answers
141 views

Optimizing code for sequence A064604

I am implementing A064604 - OEIS for positive integers up to 10 billion. I am finding the divisors in \$O(\sqrt N)\$. So, the overall time complexity of running the formula right now is \$O(N\sqrt N)\...
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1answer
335 views

Interview task to efficiently find compact representation of nodes in tree and find big O time

I recently had an interview problem where I was asked to find a compact representation of nodes in a tree. As an example, consider the following tree: ...
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2answers
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“Magic Fraction” finder

A Magic Fraction for N is one that has the following properties: It is a proper fraction (the value is < 1) It cannot be reduced further (the GCD of the numerator and the denominator is 1)...
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6answers
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Getting filtered autolist

Is there a better way to write the following code fragment? I can't have more than 10 conditional statement in my method as it gives cyclomatic complexity. ...
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2answers
2k views

Codility “max slice swap” challenge

Problem Description: Find the maximum sum of a compact subsequence of array elements after performing a single swap operation. Solution: ...
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1answer
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Is this a good Ruby implementation of Prime Factorization?

I'm doing some practice problems on Khan Academy. The current one is Prime factorization. I came up with this: ...
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1answer
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Construct KD-Tree in Java

I want to construct KD-Tree from unsorted List of points in the plane (i.e. 2-KD-Tree). To do so I used the method from Wikipedia: http://en.wikipedia.org/wiki/Kd-tree#Construction This is my code: <...
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1answer
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Russian doll envelops

Interview question from the interwebz You have a set of envelopes of different widths and heights. One envelope can fit into another if and only if both the width and height of one envelope is ...
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1answer
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Finding largest subset of line segments that don't intersect

I completed a challenge of codeeval called BayBridges. It can be found here. I have uploaded my code on GitHub here. In summary, the challenge is to take a list of line segments, each specified by ...
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2answers
91 views

Two squares or not two squares - constant time optimization

I have been trying to solve this problem, and after a bit of googling, I realised a \$O(\sqrt{n})\$ time complexity works fine (though the algorithm suggested is different from that I have used). My ...
5
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3answers
733 views

Psycho and ordinary numbers

The problem statement can be found here. In short, here's what the problem is about: You're given a set of numbers and you need to find whether the the numbers are ordinary or psycho. For a number ...
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0answers
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Proving a conjecture given a set of clauses - calculating complexity

I have written this Perl program to prove a conjecture given a set of clauses. I've actually posted some code from it on here in another question. This time its all done and I've made it as fast as ...
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3answers
740 views

Longest 'balanced' substring

I was given a task where given a string of '0's and '1's, return the longest substring where the count of '0's and '1's are equal. I was told also that the code should be O(n) and space O(1). Below ...
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1answer
104 views

Calculate difference of indices

The challenge is to reconstruct an n-digit number using the following information: On each step, you choose an index x from 1 to n. For all indices y (y < x), you calculate the difference by =...
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3answers
330 views

Performance analysis of 3 digits sum

I have a method that finds 3 numbers in an array that add up to a desired number. ...
6
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1answer
429 views

Determine total number of ways of reaching a destination

Question: One of Scotland Yard’s most wanted criminal (Mister X) is on the run and needs to reach a certain destination safely. There are three modes of transport available for him - By air, ...
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3answers
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Find all paths from source to destination

Given a directed connected graphs, find all paths from source to destination. Looking for code review, optimizations and best practices. Also need help figuring out complexity, which in my best ...
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2answers
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Genomic Range Query

Recently I worked on one of the Codility Training - Genomic Range Query (please refer to one of the evaluation report for the detail of this training). The proper approach for this question is using ...
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2answers
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2answers
795 views

'Team Split' problem

Below is my solution for this 'Team Split' problem. In summary, the problem is to find relative strength of 2 teams by finding the difference between their total strength (individual strengths can be ...
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5answers
1k views

Refactoring my problem-solution to reduce complexity

I need some help refactoring my solution to the problem below: Problem Statement An Association of Computer Scientists meets on a weekly basis. There is a certain number of seats in the meeting ...
4
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1answer
2k views

Big-O complexity calculation for a merge and sort function

I have the following code which basically takes a list of sorted integer arrays and merges them together removing the duplicates. I have tried to do the complexity analysis and came to a rough ...
13
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1answer
2k views

Nonogram puzzle solution space

I've written some code to brute-force enumerate the solution space of nonogram puzzles up to a certain size. It does a good job up to the first ~4 billion puzzles, but I run out of disk space to store ...
5
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1answer
372 views

Reducing complexity of method

I'm trying to reduce the complexity of some methods, and I'm not exactly sure what approach to take. I'm currently building a PHP wrapper for a REST API, and the main problematic class is here: https:...
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2answers
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LFU-like web caching replacement algorithm

I have implemented a simulation program that runs LRU and another web caching algorithm called Sliding Window LFU. I want to compare them both in terms of the hit rate and their run time. SW-LFU works ...
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5answers
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Checking if three numbers sum to a given number

I'm working on the following interview practice problem, and got the following solution, which runs in worst case n! time (best case constant), and I'm trying to ...
5
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1answer
306 views

Is this an efficient merge sort implementation with regards to average time complexity in Big-O notation?

Is my below merge sort implementation in O(n log n)? I am trying to implement a solution to find k-th largest element in a given integer list with duplicates with O(N*log(N)) average time complexity ...
49
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12answers
21k views

Searching in an array in less than O(n) time

I have an array where each element is either one less or one greater than the preceding element \$\{x_i = x_{i-1} \pm 1\}\$. I wish to find an element in it in less than \$O(n)\$ time. I've ...
2
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1answer
153 views

Given set of cubes can we get a given word?

Given some cubes, can cubes be arranged such that an input word can be formed from the top view of the cubes? For example: assume an imaginary cube with only 3 surfaces where ...
4
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1answer
241 views

Using Guava to reduce code complexity (and possibiliy to improve readability) of null check and assign default value

Below is my java code with some complexity, ...
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5answers
2k views

count all array[index] == index occurrences

The method foo gets a sorted list with different numbers as a parameter and returns the count of all the occurrences such that: ...
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3answers
1k views

Find all consecutive sequences in an ordered set

I have the following set. a = [1,2,3,4,5] and i want to find all of the following sequences of consecutive elements: ...
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2answers
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Fish Food Chain of complexity O(N)

I understand that if you don't know the trick, it's not easy create a solution with a complexity of \$O(N)\$. However, I would like to ask you how to solve this tricky question: You are given two ...
7
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1answer
2k views

Simplify function to sum the absolute value of the difference between all pairs of elements of a sorted array

Given a sorted array of N elements, I need to find the absolute sum of the differences of all elements. Given 4 elements (1, 2, 3 and 4): |1-2|+|1-3|+|1-4|+|2-3|+|2-4|+|3-4| = 10 Here is my code ...
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2answers
4k views

Permutation of given string

I am reading a book on DSA, and the author explains how to generate the permutation of strings using recursion. I want to know if there are better ways of doing the same, unless this is the best ...
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2answers
10k views

Fibonacci sequence implementation

This was too slow for my computer: ...
3
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1answer
183 views

Space and time complexity of operation on lists

I'm new to programming and even more new to Haskell. Below is a little tid-bit I wrote that operates on a bunch of lists. I am wondering if someone would be kind enough to walk through the function <...
6
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1answer
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Stable radix sort in-place using O(1) space

I am trying to implement a stable radix sort in place with O(1) space. I've seen Wikipedia, and I notice the C implementation is using a temporary variable to hold the sorted value for each pass, and ...

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