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‎Week 1/1. Implementing the Caesar Cipher/CaesarCipher.java

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import edu.duke.*;
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public class CaesarCipher
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{
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public String encrypt(String input, int key)
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{
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StringBuilder encrypted = new StringBuilder(input);
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String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
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String shiftedAlphabet = alphabet.substring(key) + alphabet.substring(0, key);
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for(int i=0; i<encrypted.length(); i++)
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{
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char currChar = encrypted.charAt(i);
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int idx = alphabet.indexOf(currChar);
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if(idx != -1) //...currChar is an ALPHABET...//
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{
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char newChar = shiftedAlphabet.charAt(idx);
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encrypted.setCharAt(i, newChar);
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}
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else //...for lowercase...//
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{
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currChar = Character.toUpperCase(currChar);
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idx = alphabet.indexOf(currChar);
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if(idx != -1)
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{
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char newChar = shiftedAlphabet.charAt(idx);
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newChar = Character.toLowerCase(newChar);
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encrypted.setCharAt(i, newChar);
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}
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}
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}
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return encrypted.toString();
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}
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public String encryptTwoKeys (String input, int key1, int key2)
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{
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StringBuilder encrypted = new StringBuilder(input);
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String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
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String shiftedAlphabetKey1 = alphabet.substring(key1) + alphabet.substring(0, key1);
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String shiftedAlphabetKey2 = alphabet.substring(key2) + alphabet.substring(0, key2);
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for(int i=0; i<encrypted.length(); i++)
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{
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if(i%2==0)
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{
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char currChar = encrypted.charAt(i);
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int idx = alphabet.indexOf(currChar);
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if(idx != -1) //...currChar is an ALPHABET...//
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{
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char newChar = shiftedAlphabetKey1.charAt(idx);
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encrypted.setCharAt(i, newChar);
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}
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else //...for lowercase...//
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{
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currChar = Character.toUpperCase(currChar);
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idx = alphabet.indexOf(currChar);
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if(idx != -1)
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{
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char newChar = shiftedAlphabetKey1.charAt(idx);
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newChar = Character.toLowerCase(newChar);
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encrypted.setCharAt(i, newChar);
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}
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}
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}
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else
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{
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char currChar = encrypted.charAt(i);
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int idx = alphabet.indexOf(currChar);
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if(idx != -1) //...currChar is an ALPHABET...//
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{
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char newChar = shiftedAlphabetKey2.charAt(idx);
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encrypted.setCharAt(i, newChar);
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}
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else //...for lowercase...//
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{
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currChar = Character.toUpperCase(currChar);
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idx = alphabet.indexOf(currChar);
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if(idx != -1)
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{
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char newChar = shiftedAlphabetKey2.charAt(idx);
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newChar = Character.toLowerCase(newChar);
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encrypted.setCharAt(i, newChar);
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}
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}
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}
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}
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return encrypted.toString();
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}
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//////////////////////////////////////////////////////////////////////////////////////
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public void testCaesar()
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{
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//FileResource fr = new FileResource();
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//String message = fr.asString();
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//String encrypted = encrypt(message, 23);
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//System.out.println("key is " + 23 + "\n" + encrypted);
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//System.out.println("ENCRYPTED: " + encrypt("At noon be in the conference room with your hat on for a surprise party. YELL LOUD!",15));
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System.out.println("ENCRYPTED: " + encryptTwoKeys("At noon be in the conference room with your hat on for a surprise party. YELL LOUD!", 8, 21));
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}
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//////////////////////////////////////////////////////////////////////////////////////
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public static void main (String[] args)
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{
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CaesarCipher CIPHER = new CaesarCipher();
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CIPHER.testCaesar();
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}
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}

‎Week 1/1. Implementing the Caesar Cipher/WordPlay.java

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import edu.duke.*;
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public class WordPlay
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{
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public boolean isVowel(char ch)
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{
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String vowels = "aeiouAEIOU";
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if(vowels.indexOf(ch) != -1)
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{
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return true;
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}
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return false;
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}
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public String replaceVowels (String phrase, char ch)
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{
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StringBuilder result = new StringBuilder(phrase);
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for(int i=0; i<result.length(); i++)
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{
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if(isVowel(result.charAt(i)))
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{
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result.setCharAt(i,ch);
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}
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}
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return result.toString();
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}
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public String emphasize (String phrase, char ch)
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{
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StringBuilder result = new StringBuilder(phrase);
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for(int i=0; i<result.length(); i++)
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{
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if(result.charAt(i) == ch || result.charAt(i) == Character.toUpperCase(ch))
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{
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if(i%2 == 0) //...even index, but odd number location
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{
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result.setCharAt(i,'*');
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}
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else
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{
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result.setCharAt(i,'+');
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}
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}
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}
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return result.toString();
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}
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//////////////////////////////////////////////////////////////////////////////////////
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public void testisVowel()
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{
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System.out.println("F is vowel..?" + isVowel('a'));
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}
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public void testreplaceVowels()
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{
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System.out.println("Hello World replaced vowels: " + replaceVowels("Hello World",'*'));
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}
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public void testemphasize()
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{
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System.out.println("Mary Bella Abracadabra: " + emphasize("Mary Bella Abracadabra",'a'));
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}
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//////////////////////////////////////////////////////////////////////////////////////
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public static void main (String[] args)
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{
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WordPlay CIPHER = new WordPlay();
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CIPHER.testisVowel();
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CIPHER.testreplaceVowels();
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CIPHER.testemphasize();
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}
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}

‎Week 1/2. Breaking the Caesar Cipher/CaesarBreaker.java

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//import edu.duke.FileResource;
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public class CaesarBreaker
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{
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public String decrypt(String encrypted)
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{
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CaesarCipher cc = new CaesarCipher();
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int[] freqs = countLetters(encrypted);
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int maxDex = maxIndex(freqs);
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int dkey = maxDex-4;
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if(maxDex < 4)
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{
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dkey = 26-(4-maxDex);
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}
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System.out.println("Key is " + dkey);
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return cc.encrypt(encrypted, 26-dkey);
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}
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public int[] countLetters(String message)
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{
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String alphabet = "abcdefghijklmnopqrstuvwxyz";
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int[]counts = new int[26];
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for(int i=0; i<message.length(); i++)
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{
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char ch = Character.toLowerCase(message.charAt(i));
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int dex = alphabet.indexOf(ch);
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if(dex != -1)
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{
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counts[dex]+=1;
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}
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}
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return counts;
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}
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public int maxIndex(int[] counts)
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{
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int max = 0;
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for(int i=1; i<counts.length; i++)
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{
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if(counts[i] > counts[max])
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{
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max = i;
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}
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}
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return max;
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}
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//////////////////////////////////////////////////////////////////////////////////////////////////////
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public String halfOfString (String message, int start)
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{
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String res = "";
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for(int i=start; i<message.length(); i+=2)
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{
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res += message.charAt(i);
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}
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return res;
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}
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public int getKey(String s)
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{
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int[] freqs = countLetters(s);
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int maxDex = maxIndex(freqs);
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int dkey = maxDex-4;
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if(maxDex < 4)
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{
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dkey = 26-(4-maxDex);
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}
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return dkey;
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}
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public String decryptTwoKeys (String encrypted)
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{
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String encrypted1 = halfOfString(encrypted, 0);
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String encrypted2 = halfOfString(encrypted, 1);
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int key1 = getKey(encrypted1);
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int key2 = getKey(encrypted2);
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CaesarCipher cc = new CaesarCipher();
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return cc.encryptTwoKeys(encrypted, 26-key1, 26-key2);
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}
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/////////////////////////////////////////////////////////////////////////////////////////////////////////////////
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void testCaesarBreaker()
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{
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System.out.println("DECRYPTED: " + decrypt("Yjhi p ithi higxcv lxiw adih du ttttttttttttttttth"));
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}
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void testhalfOfString()
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{
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System.out.println("HALF: " + halfOfString("Qbkm Zgis", 1));
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}
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void testdecryptTwoKeys()
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{
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System.out.println("HALF: " + decryptTwoKeys("Gwpv c vbuq pvokki yfve iqqu qc bgbgbgbgbgbgbgbgbu"));
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}
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//////////////////////////////////////////////////////////////////////
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public static void main (String[] args)
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{
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CaesarBreaker TESTCASE = new CaesarBreaker();
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//TESTCASE.testCaesarBreaker();
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//TESTCASE.testhalfOfString();
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TESTCASE.testdecryptTwoKeys();
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}
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}

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