# Blog

## Programming Interview Question - Merge Intervals (InterviewCake#4)

Programming Interview Question - Merge Intervals

This post will explore the solutions to the question #4 of the famous website cakeinreview (here the link).

Programming Interview Question - Merge Intervals - Problem Statement

Given a list of pair of integers return a list of merged or condensed intervals.

Given for instance the following input list

Your function should take care of corner cases like merging two intervals like the following in . Give a solution first. Then try to solve it in .

Read More »Programming Interview Question - Merge Intervals (InterviewCake#4)

# Tower of Hanoi - C++

This brief article is about the tower of Hanoi. Wrote this super simple C++ for a student and thought maybe it could be helpful.

It works on the idea that in order to move n disks from pile 1 to 3 we need to first move the first disks to a support pole (choosing the right on is part of the solution, see the code for further detail), then move disk in the correct position, and finally move the first disks from support pole to the correct location. Let the recursion does the magic!

The base case is when we have only one disk to move. Simply move the disk in the correct pile.

Tower of Hanoi - C++ Code

Read More »Tower of Hanoi - C++

# Construct a Binary Tree from its inorder and preorder

This article will investigate the problem of reconstructing a binary tree given its inorder and preorder traversal.

Let's say for instance that we have the following binary tree (see figure)

Binary Tree

which has the following in order and preorder traversal respectively.

Given IN and PRE how can we construct the original tree?

The key idea is to observe that the first element in is the root of the tree and that the same element appears somewhere in , let's say at position . This means that in order traversal has processed k element before to process the root, meaning that the number of nodes of the left tree of the root is . Obviously, if the first element belongs to the left subtree then all the others belongs to the right tree.

We will use this idea to write a recursive algorithm that builds the tree starting from its traversals. The algorithm works as follows:Read More »Construct a binary Tree from its inorder and preorder traversal

## List Cycle Detection

List Cycle Detection Linked list cycle detection problem is a very instructive and fun problem to reason about. This article will state the problem first and then explains how we can solve it efficiently while giving some insight on the underlying math. A list can gets corrupted and some node can be linked by more than one node, as in the following figure. This could lead to never ending traversal of the list. So it make sense to solve the following problem: List Cycle Detection - Problem Statement Given  a linked list, detect if the list is circular i.e. contains a cycle Find the starting… Read More »List Cycle Detection

# HOW-TO: Dynamic Message of the day

The final result will be something like the following:

It mixes a fun message using fortune and cowsay which you can install using


sudo dnf install fortune-mod cowsay



utility and some informative info about the status of the system as:

• Ram and Swap available and used
• Disk space

The script file can be easily configured and extended to suits the your needs. Colors can also be easily customized.

Read More »Dynamic Message of the Day - motd - Fedora Linux

# Distributed  Hadoop and HBase installation - Fedora Linux

In this post I will describe how to get started with the latest versions of hadoop and hbase describing all the step to obtain a working hadoop installation. The steps described here can be easily used to perform a working installation on a large cluster (even tough it can requires additional steps as shared filesystem for instance).

## Prerequisites

 sudo dnf install openssh openssh-askpass openssh-clients openssh-server

Don't forget to start the ssh service using the following command:

 sudo service sshd start

# Programming Inteview Question

## Then if  holds, the entire rows  and column  are set to .

For examples if the following is used as input matrix

4 9 14 19 24
3 8 13 18 23
2 7 12 17 22
1 6 11 16 21
0 5 10 15 20

using  the following  equality predicate (==3) (i.e. returns true if the passed parameter is 3) and  the resulting matrix is:

-1 9 14 19 24
-1 -1 -1 -1 -1
-1 7 12 17 22
-1 6 11 16 21
-1 5 10 15 20

Hint use template for make the procedure as general as possible.

## Programming Inteview Question Solution

Read More »Programming Interview Question - Set Row and Column if - C/C++

# Question: Given a square matrix of size M and type T, rotate the matrix by 90 degrees counterclockwise in place.

For example the algorithm should return the right matrix if is left one is passed as input.

0 1 2 3 4
5 6 7 8 9
10 11 12 13 14
15 16 17 18 19
20 21 22 23 24
4 9 14 19 24
3 8 13 18 23
2 7 12 17 22
1 6 11 16 21
0 5 10 15 20

## Solution:

Read More »Programming Inteview Question - Rotate Matrix - C/C++

# Programming Interview Question

## Question: given two string write a method to decide if one is a permutation of the other.

This is a common question that could be easily solved if we know in advance which is the size of the alphabeth. A straightforward approach could be to sort both strings and then compare them. This approach has complexity  due to sorting. We can do better and lower the complexity to  if we reason as follows: given a boolean sequence of the same size of the alphabet  initially false initialized.  Then what happen if  for each char we found in the  string  we negate the value of the correnspoding bool in the sequence? We end up having the  at position  if the char  appeared an odd number of times and  otherwise. Now if the other string  is a permutation of the first one, we all agree that for each char in  it contains the same number of occurrences. This means that if we apply the same process as before on the boolean sequence using as input the string  each bool is being negated an even number of times and this means that its value would be the same as the beginning of the process (all ). So if the sequence does not contains any true value, than it means that the strings contains the same elements i.e. they are permutation of each other.

Example:

1. "abbccd" ,  "cbdabc" , 
2. Apply negation using s
• 
3. Apply negation using v
• 

A possible C++ implementation is shown here

Read More »Programming Interview Question - String Permutation Test - C++

# Programming Intervew Question: Unique Characters in a String

##### Question: implement an algorithm to determine if a string has all unique characters

The idea behing this (fairly easy) question is that whenever we found that any chars is repeated at least twice we should return false. In order to do that we have to look at each char we are loloking for a solution which complexity is at least . We are free to use any support data structure. is the size of the ASCII charset.

Read More »Programming Interview Question- Unique Characters in a string - C++