Find Sum (i … j) in a list

The problem is to sum the ith to jth element of a given list. The easiest solution runs in \mathcal{O}(n) time, which starts are the ith index and adds up the numbers in the list until it reaches the jth index. In this post i will show the process of calculating the sum of elements i through j both inclusive (where i \le j), which takes \mathcal{O}(1) time for finding the sum, and \mathcal{O}(n) time and space for preprocessing the given list of length n.
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Find a String in an Alphabet Grid

Everybody of us has definitely played the word search game in which a grid of characters are given, and a list of words are given which are to be found in the grid horizontally, vertically or diagonally. In this post i will show a simple solution to a more generalized version of the search which finds the strings in the grid with backtracking.
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Towers of Hanoi Iterative process: simulating recursion

The last post Recursive Solution to Towers of Hanoi described the well-known recursive definition and implementation of the Towers of Hanoi problem. This post is an extension presenting the same problem iteratively by simulating the recursion stack. This implementation will simply to simulate the recursion presented on the previous post by using an explicit manual stack.

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Recursive Solution to Towers of Hanoi

Towers of Hanoi is a mathematical game or a puzzle in which there are three pegs, and some disks (originally 8) of different radius placed on top of one another such that no larger disk is placed on a smaller disk. The task is to transfer such a column of disks from a source peg to another destination peg. The constraints are we can move only one disk at a time, and we may use the third peg as a temporary storage for the disks, and a larger disk cannot be placed on top of a smaller disk.

The puzzle was invented by the French mathematician Édouard Lucas in 1883. There is a legend about an Indian temple which contains a large room with three time-worn posts in it surrounded by 64 golden disks. Brahmin priests, acting out the command of an ancient prophecy, have been moving these disks, in accordance with the rules of the puzzle, since that time. The puzzle is therefore also known as the Tower of Brahma puzzle. According to the legend, when the last move of the puzzle is completed, the world will end.[2] It is not clear whether Lucas invented this legend or was inspired by it.


In this post I will describe the basic recursive solution to the Towers of Hanoi
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Simple script to restart services automatically when stopped in Fedora/Redhat

fedora_logoWhen occasionally the services like Apache or MySQL or other rc.d script crashes and stops working, then instead of restarting them manually, it may be more desirable to restart them automatically. A friend of mine asked about such an issue and here is the quick fix bash script fix.

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Accessing private data members directly outside from its class in C++

Private members in C++ cannot be accessed from outside the class directly. In this post I will tell an interesting fact, that in C++ however there are means with which you can access/modify the values of the private members of a class from outside of the class, when the structure of the class is known.

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Bash Script: Reading ID3v1 Tags

mp3 files contain track name, artist name, etc meta data about the music file itself. The meta data format used in mp3 files are called the ID3 tags. There are different versions of ID3 tags available. The objective is to read this meta data information from an mp3 file having an ID3v1 tag.

A detailed overview of the ID3v1 (as well as ID3v2 tags) are done here in this post: What are ID3 Tags all about?. A small ID3v1 library is also implemented (reading and writing tags) in C language here: An ID3v1 Tag Parsing Library. TagLib is available to read and write ID3v1 and ID3v2 tags and is free to use.
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