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Caesar.java
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140 lines (117 loc) · 4.54 KB
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package com.thealgorithms.ciphers;
import java.util.Scanner;
/**
* A Java implementation of Caesar Cipher. /It is a type of substitution cipher
* in which each letter in the plaintext is replaced by a letter some fixed
* number of positions down the alphabet. /
*
* @author FAHRI YARDIMCI
* @author khalil2535
*/
public class Caesar {
/**
* Encrypt text by shifting every Latin char by add number shift for ASCII
* Example : A + 1 -> B
*
* @return Encrypted message
*/
public static String encode(String message, int shift) {
StringBuilder encoded = new StringBuilder();
shift %= 26;
final int length = message.length();
for (int i = 0; i < length; i++) {
// int current = message.charAt(i); //using char to shift characters because ascii
// is in-order latin alphabet
char current = message.charAt(i); // Java law : char + int = char
if (IsCapitalLatinLetter(current)) {
current += shift;
encoded.append((char) (current > 'Z' ? current - 26 : current)); // 26 = number of latin letters
} else if (IsSmallLatinLetter(current)) {
current += shift;
encoded.append((char) (current > 'z' ? current - 26 : current)); // 26 = number of latin letters
} else {
encoded.append(current);
}
}
return encoded.toString();
}
/**
* Decrypt message by shifting back every Latin char to previous the ASCII
* Example : B - 1 -> A
*
* @return message
*/
public static String decode(String encryptedMessage, int shift) {
StringBuilder decoded = new StringBuilder();
shift %= 26;
final int length = encryptedMessage.length();
for (int i = 0; i < length; i++) {
char current = encryptedMessage.charAt(i);
if (IsCapitalLatinLetter(current)) {
current -= shift;
decoded.append((char) (current < 'A' ? current + 26 : current)); // 26 = number of latin letters
} else if (IsSmallLatinLetter(current)) {
current -= shift;
decoded.append((char) (current < 'a' ? current + 26 : current)); // 26 = number of latin letters
} else {
decoded.append(current);
}
}
return decoded.toString();
}
/**
* @return true if character is capital Latin letter or false for others
*/
private static boolean IsCapitalLatinLetter(char c) {
return c >= 'A' && c <= 'Z';
}
/**
* @return true if character is small Latin letter or false for others
*/
private static boolean IsSmallLatinLetter(char c) {
return c >= 'a' && c <= 'z';
}
/**
* @return string array which contains all the possible decoded combination.
*/
public static String[] bruteforce(String encryptedMessage) {
String[] listOfAllTheAnswers = new String[27];
for (int i=0; i<=26; i++) {
listOfAllTheAnswers[i] = decode(encryptedMessage, i);
}
return listOfAllTheAnswers;
}
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int shift = 0;
System.out.println("Please enter the message (Latin Alphabet)");
String message = input.nextLine();
System.out.println(message);
System.out.println("(E)ncode or (D)ecode or (B)ruteforce?");
char choice = input.next().charAt(0);
switch (choice) {
case 'E':
case 'e':
System.out.println("Please enter the shift number");
shift = input.nextInt() % 26;
System.out.println(
"ENCODED MESSAGE IS \n" + encode(message, shift)); // send our function to handle
break;
case 'D':
case 'd':
System.out.println("Please enter the shift number");
shift = input.nextInt() % 26;
System.out.println("DECODED MESSAGE IS \n" + decode(message, shift));
break;
case 'B':
case 'b':
String[] listOfAllTheAnswers = bruteforce(message);
for (int i =0; i<=26; i++) {
System.out.println("FOR SHIFT " + String.valueOf(i) + " decoded message is " + listOfAllTheAnswers[i]);
}
default:
System.out.println("default case");
}
input.close();
}
}