### Data decryption using Caesar Cipher

In the previous blog post we discussed about Encryption of a file using Caesar Cipher, in this post we discuss a method to decrypt the same file. If you want to view the previous post on Encryption using Caesar Cipher click HERE.

Decryption is a process of decoding the encrypting the encrypted file, to do this we need to know 2 things, the first is the method of encryption and the second is cipher key which in this case is our shift value. once we know these things we can start deciphering the files.
As caesar cipher is a substitution cipher, shift value decides which value is replaced with another value, in encryption we replace each letter by the letter to its right by shift value position, hence now we need to do the opposite, we have to replace each letter by the letter to its left by shift value positions.

So for shift value of 3 we have,
Plaintext :          ABCDEFGHIJKLMNOPQRSTUVWXYZ
decipher text :    XYZABCDEFGHIJKLMNOPQRSTUVW

Hence every 'a' in our message is replaced by 'x' if the shift value is 3.

consider, Plaintext :  "KHOOR, ZHOFRPH WR PB EORJ" will be changed to
Ciphertext: "HELLO, WELCOME TO MY BLOG"

Instead of using only the 26 letters I have also included spaces, symbols and numbers in my cipher hence The following is my keyspace,
"0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!"#\$%&'( )*+,-./"

In this program we use the same approach as we have used in the encryption code, We have a method that accepts a string and shift value and return a decrypted string. Then we have a method that accepts the path of encrypted file, it reads all the data from that file and sends it to the decryption method and finally makes a file with decrypted message and stores it on the desktop.

Lets get to the code,

Below is the implementation code in cpp, java, python.

### Sample input and output to check the program

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### Infix to Prefix conversion using Stack

This post is about conversion of Infix expression to Prefix conversion. For this conversion we take help of stack data structure, we need to push and pop the operators in and out of the stack.

Infix expressions are the expressions that we normally use,eg. 5+6-7; a+b*c etc. Prefix expressions are the expressions in which the 2 operands are preceded by the operator eg. -+567 , +a*bc etc.

This method is very similar to the method that we used to convert Infix to Postfix but the only difference is that here we need to reverse the input string before conversion and then reverse the final output string before displaying it.

NOTE: This changes one thing that is instead of encountering the opening bracket we now first encounter the closing bracket and we make changes accordingly in our code.

So, to convert an infix expression to a prefix expression we follow the below steps
(we have 2 string, 1st is the input infix expression string 2nd is the output string which is empty initially)

We first revers…

Hashing is a technique used for storing , searching and removing elements in almost constant time. Hashing is done with help of a hash function that generates index for a given input, then this index can be used to search the elements, store an element, or remove that element from that index.

A hash function is a function that is used to map the data elements to their position in the data structure used. For example if we use an array to store the integer elements then the hash function will generate position for each element so that searching, storing and removing operation on the array can be done in constant time that is independent of the number of elements in the array. For better look at the example below.

now we face a problem if for 2 numbers same position is generated example consider elements 1 and 14

1 % 13 = 1

14 % 13 = 1

so when we get 1 we store it at the first position, but when we get 14 we see that the position 1 is already taken, this is a case of collision.

Inorder…