Cipher.java

import java.io.*;
import java.util.*;

public class Cipher {
    protected double[] CorpusFreqs = new double[26];
    protected double totalChars=0;
    protected String alpha = "abcdefghijklmnopqrstuvwxyz";
    
    //for encoded string
    protected double[] freqs = new double[26];
    protected double total=0;

    protected double[] rotvalues = new double[26];

    public String encode(String s, int rot) {
	String lower = s.toLowerCase();
	String coded = "";
	char c;
	rot = rot%26;
	for (int i=0; i<lower.length(); i++) {
	    c = lower.charAt(i);
	    if (c >= 97 && c <= 122) {
		c = (char)(c + rot);
		if (c > 122) {
		    c = (char)(c - 26);
		}
		else if (c < 97) {
		    c = (char)(c + 26);
		}
	    }
	    coded = coded + c;
	}
	return coded;
    }

    public void buildCorpusFreq(String filename) {
	try {
	    Scanner sc =  new Scanner (new File(filename));
	    while (sc.hasNext()) {
		String s = sc.nextLine();
		s = s.toLowerCase();
		for (int i=0; i<s.length(); i++) {
		    char c = s.charAt(i);
		    if (c >= 'a' && c <= 'z') {
			CorpusFreqs[c-'a'] = CorpusFreqs[c-'a']+1;
			totalChars = totalChars + 1;
		    }
		}
	    }
	} catch (Exception e) {}
    }

    public double getVect(char c,double[] array,double t) {
	double n = array[c-'a'];
	return n/t;
    }

    public String cracker(String s) {
	double sum;
	double value;
	//no rotation...rotation:
	for (int i=0; i<26; i++) {
	    //each letter:
	    sum = 0;
	    for (int i2=0; i2<26; i2++){
		sum+=Math.pow((getVect(alpha.charAt(i2),CorpusFreqs,totalChars) + getVect(alpha.charAt(i2),freqs,total)),2);
	    }
	    double r = Math.sqrt(sum);
	    rotvalues[i] = r;
	}
	int min = 0;
	for (int i3=1;i3<26;i3++){
	    if (rotvalues[i3] < rotvalues[min])
		min = i3;
	}
	return encode(s, -min);
    }
    
    public void codeFreqs(String s) {
	String lower = s.toLowerCase();
	for (int i=0; i<lower.length(); i++) {
	    char c = s.charAt(i);
	    if (c >= 'a' && c <= 'z') {
		freqs[c-'a'] = freqs[c-'a']+1;
		total++;
	    }
	}
    }


}