# c++

## The most asked coding interview - #5

Transform array such that each element contains the greatest element on its right side Problem statement In this article we will be discussing how to solve an easy problem that has been asked at Amazon coding interviews. This is a must do problem for your coding interview preparation. The problem statement goes as follows: You are given an array A of size N. You have to modify A in place s.t. A[i] = M where M is the maximum value among all elements A[j], j > i. If such element does not exists set A[i] = -1. Example Solution Since this is a quite easy… Read More »The most asked coding interview - #5

# Return the Maximum absolute difference of values and indices

The problem statement goes as follows:

## Problem statement

Given an array A determine the maximum possible value of the following expression:
$f(i,j) =| A[i]-A[j] | +|i-j|$

## Example

Input : A = {1, 3, -1}
Output : 5
because the maximum value obtainable is:
=> f(1,2) = |3 - (-1)| + |1-2| = 5

Input : A={3, -2, 5, -4}
Output : 10
=> f(1, 4) = f(4, 1) = |3 - (-4)| + |1 - 4| = 10
Note that in this case we can also obtain 10 from
=> f(3, 4) = f(4, 3) = |5 - (-4)| + |3 - 4| = 10


Sort an array of size N made of numbers from 0 to K Problem statement In this article we will be discussing another (see the previous article) very popular programming interview question. This time we are asked to sort an array of size N whose elements are in the range [0,K). Problem statement Given an array $A=[a_1,a_2,…a_n],\: 1 \leq a_i \leq K$ modify A s.t. it is sorted. As usual you should ask your interviewer some clarifying questions. For example a sensible question to ask could be: What is the maximum value of $K$ and of $N$? Let's assume that $N \leq 10^7$ and $K\leq… Read More »The most asked programming interview questions - #3 ## The most asked coding interview - #2 # Coding interview question: Determine if number is an Armstrong number ## Problem statement In this article we will be discussing another (see the previous article counting triples with a given sum) of the most common coding interview questions. The problem statement is really simple and goes as follows: Given an positive integer N determine if it is an Armstrong number? A number$x_1x_2…x_n$(1 \leq x_i \leq 9$ is a digit ) of length $n$ is an Armstrong number if the following is true:
$x_nx_{n-1}…x_2x_1 = pow(x_1,n) + pow(x_2,n) + … pow(x_n,n)$

In other words if raising all digits to power $n$ and sum all them up you obtain the original number, then $N$ is an Armstrong number.

## Apply a permutation to a vector

In this article we are going to discuss an interview question that is asked quite frequently in companies like Facebook, Microsoft, or Google. The problem statement goes as follows: Given an vector<T> A of elements of type T of length Nand a vector<size_t> P where Pis a permutation of numbers from [0-N-1]you need to apply the permutation Pto the vector A. You are not allowed to use more than O(1) additional space. For example suppose A=['a','b','c','d'] and P=['2','0','4','1']. After applying P to A, the latter becomes: ['c','a','d','b']. P[i] basically tell you which element of A should go in position i in the final arrangement of… Read More »Apply a permutation to a vector

## C++ - Simple command line argument manager

Command-line argument management is tricky to get right especially when the number of options that we support and the number of their combination is big. For this kind of applications, there are already a number of very effective libraries and tools supporting the programming in such a scenario. One such library is Boost::program_options which I highly encourage you to use as is it awesome. But there are other cases where we need to quickly write a prototype or when the number of options and possible configuration is small where using Boost could be overkill. In such cases what we usually do is writing ad-hoc command-line… Read More »C++ - Simple command line argument manager

## Modern C++ concurrency - parallel quick-sort with std::future

In this short lesson we will discuss how to parallelize a simple and rather inefficient (because this is not an in-place version) implementation of quick-sort using asynchronous tasks and futures. We will perform some benchmarking and performance analysis and we will try to understand how we can further improve our implementation. Quick sort In this section, I will briefly refresh your memory on quick-sort. I will do so by showing you a simple and self-explicative Haskell version first. We will also write a C++ (serial) version of the same code implementation C++ that we will use as a basis for our parallelization. Here it goes… Read More »Modern C++ concurrency - parallel quick-sort with std::future

## Introduction

In this lesson we will talk about a way of returning values from threads, more precisely we will talk about std::future which is a mechanism that C++ offers in order to perform asynchronous tasks and query for the result in the future.
A future represents an asynchronous task, i.e. an operation that runs in parallel to the current thread and which the latter can wait (if it needs to) until the former is ready.
You can use a future all the time you need a thread to wait for a one-off event to happen. The thread can check the status of the asynchronous operation by periodically polling the future while still performing other tasks, or it can just wait for the future to become ready.

Read More »Modern C++ concurrency - Returning values from Threads - std::future

## Introduction

In the previous lesson we have seen how data can be protected using mutex. We now know how to make threads do their work concurrently without messing around with shared resources and data. But sometimes we need to synchronize their actions in time, meaning that we might want a thread t1 to wait until a certain condition is true before allowing it to continue its execution.

This lesson discusses the tools that we can use to achieve such behavior efficiently using condition variables.