Caesar Cipher - I made this caesar cipher decrypter to solve hackerrank.com puzzles.

CaesarCipher.java

import java.util.Scanner;


public class CaesarCipher {

	private static char []letters = 
	{	 'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'
		,'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'
		,'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'
	};
	
	public static void main(String args[]){
		Scanner in = new Scanner(System.in);
		
		System.out.println("Encrypted Word");
		String encryptedAnswer = in.nextLine();
		System.out.println("Decrypted Word");
		String decryptedAnswer = in.nextLine();
		System.out.println("String to decode:");
		String encryptedString = in.nextLine();
		String decryptedString = "";
		int diff = 0;
		
		
		//calculate difference between letters
		encryptedAnswer = encryptedAnswer.toLowerCase();
		decryptedAnswer = decryptedAnswer.toLowerCase();
		
		char enfirst = encryptedAnswer.charAt(0);
		char defirst = decryptedAnswer.charAt(0);
		
		int e = (int) enfirst;
		int d = (int) defirst;
		
		//get difference between the 2 letters
		diff = d - e;
		//System.out.println("diff = " + diff);
		System.out.println(encryptedString);
		
		int startMiddleLetters = 26;
		
		//decrypt string
		for(int i = 0; i < encryptedString.length();i++){
			//get current char
			char curChar = encryptedString.charAt(i);
			
			if(curChar != ' ' && curChar != ',' && curChar != '-'){
				//Get number of current char
				int curCharInt = (int)curChar;
				//Calculate position of the current char in the middle section of the letters array
				int posOfCurCharInLettersArray = (curCharInt - 97) + startMiddleLetters; //97 is 'a' in ascii
				//get position of decrypted char
				int posOfNewCharInLettersArray = posOfCurCharInLettersArray + diff;
				//get decrypted char
				char newChar = letters[posOfNewCharInLettersArray];
				
				//build output string
				decryptedString += newChar;
			}else{
				//build output string
				decryptedString += curChar;
			}
			
		}
		
		//output decrypted string
		System.out.println(decryptedString);
		
	}
}

To become a beta user of hackerrank.com, you have to solve 100 puzzles... all of which use the Caesar Cipher.
To make things quicker, I created this...

I struggled for a while getting stringIndexOutOfBounds error because there was my ASCII calculations were off, then realised if I had a char array with 3 sets of letters from(a -> z), then by referencing the middle set of letters, it would be very easy to add and subtract the index without getting errors.

• It made things look a bit cleaner :D

great work on this!

I made a few modifications in my fork including the use of command line arguments, a StringBuffer, and modulus arithmetic to simplify the letters char array.

:: devon