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Copy pathCaesarCipher.java
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40 lines (38 loc) · 1.57 KB
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import edu.duke.*;
public class CaesarCipher {
public String encrypt(String input, int key) {
//Make a StringBuilder with message (encrypted)
StringBuilder encrypted = new StringBuilder(input);
//Write down the alphabet
String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
//Compute the shifted alphabet
String shiftedAlphabet = alphabet.substring(key)+
alphabet.substring(0,key);
//Count from 0 to < length of encrypted, (call it i)
for(int i = 0; i < encrypted.length(); i++) {
//Look at the ith character of encrypted (call it currChar)
char currChar = encrypted.charAt(i);
//Find the index of currChar in the alphabet (call it idx)
int idx = alphabet.indexOf(currChar);
//If currChar is in the alphabet
if(idx != -1){
//Get the idxth character of shiftedAlphabet (newChar)
char newChar = shiftedAlphabet.charAt(idx);
//Replace the ith character of encrypted with newChar
encrypted.setCharAt(i, newChar);
}
//Otherwise: do nothing
}
//Your answer is the String inside of encrypted
return encrypted.toString();
}
public void testCaesar() {
int key = 17;
FileResource fr = new FileResource();
String message = fr.asString();
String encrypted = encrypt(message, key);
System.out.println(encrypted);
String decrypted = encrypt(encrypted, 26-key);
System.out.println(decrypted);
}
}