Three difficult HackerRank problems and how to solve them

Coding Challenge Coding Live

Time complexity is O(N*log(N)) and space complexity is O(1).

Time complexity is O(N) and space complexity is O(1).

If exactly one character has a different count than all other characters, then Keysel says to remove this character completely to fix S.

If two or more have less or more characters, then there is no way to fix the string in just one removal.

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Insertion Sortis a simple sorting technique. Sometimes arrays may be too large for you to wait around for insertion sort to finish, so Kysel suggests another way that you can calculate the number of times Insertion Sort shifts each element when sorting an array.

Here are some of the more difficult sample HackerRank coding exercises and solutions fromMartin Kysel, a Cambridge, Massachusetts-based software engineer at NuoDB, which runs an elastic SQL database for cloud applications.

Often for basic exercises the first result is the question, and the second result is the solution, which seems easy, but you have to double-check that the solution is correct. In addition, you can rarely find solutions to the most challenging coding exercises online, especially since firms usually write their own questions and exercises.

There is just lots of code, but the actual solution is pretty simple, according to Keysel. First, you extract layers to simplify the logic. Then, you rotate the layers similarly to theCodility Rotationchallenge.

Searching for a 10 lines long paragraph in Google is not an acceptable option, especially since the HackerRank website disables copy/paste in the description area. A workaround is to search for the title of the exercise, which uniquely identifies a question on HackerRank and will be mentioned in related solutions posted online, making it perfect for being indexed by Google, according toThe HFT Guy, a London-based developer who has worked at high-frequency trading shops.

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There are more solutions with nlogn time for this challenge. Kysel decided to use Binary Indexed Trees as they are a data structure I am not that familiar with. The other solution includes a modified merge-sort that is posted as the problem editorial. BITs are effective for computing cumulative frequencies in log(N) time and are therefore perfectly suited for this problem. They assume a full tree and therefore are bound to the maximal range defined in the problem specification.

If ki is the number of elements over which the ith element of the array has to shift, then the total number of shifts will be k1 +k2 ++kN.

To complete theSherlock and Valid Stringexercise, you need to know that a valid string is a string S such that for all distinct characters in S each such character occurs the same number of times in S.

Cannot load job sectors at this time

In theAlgo Matrix Rotationexercise, you are given a 2D matrix, a, of dimension MxN and a positive integer R. You have to rotate the matrix R times and print the resultant matrix. Rotation should be in a counter-clockwise direction.

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To get a job as acomputer programmeronWall Streetor in the City, you may have to pass a HackerRank test. Last time we looked, Goldman Sachs, Morgan Stanley, Bank of America, Bloomberg, BNY Mellon and Deutsche Bank wereall signed-up,as was the hedge fund Two Sigma.There are typically three types of problems that youll have to deal with: multiple-choice questions, a SudoRank exercise and a coding exercise. Here are tips for how to solve the latter.

Keysel optimized this solution to the minimal case that passes all tests on HackerRank. It seems that each character occurs one or two times. The logic of Keysels solution is based on character counts.

HackerRank exercises can be difficult.

If they are all equal, then all characters occur exactly N times and there is no removal needed.

Time complexity is O(NM) and space complexity is O(NxM).

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