public static void estimateKeyLength(String cipherText, int suggestLength){

        double[] ic;
        for(int i=1;i<=suggestLength;i++){
             ic = new double[i];
             ic= subSequence(cipherText,i);
            System.out.print("Klucz o długości "+i+": ");
                for(int j=0;j<ic.length;j++){
                    System.out.print(ic[j]+" ");
                }
                System.out.println();
            }
    }

    public static double[] subSequence(String text, int k) {
        String sub = "";
        double[] ic = new double[k];
        for (int i = 0; i < k; i++) {
            for (int j = i; j < text.length(); j += k) {
                sub += text.substring(j, j + 1);
            }
            ic[i]=indexOfCoincidence(frequencyAnalysis(sub),sub.length());
            sub = "";
        }
        return ic;
    }

    public static int[] frequencyAnalysis(String text){
        int [] frequencies = new int[26];

        for(int i=0;i<text.length();i++){
            frequencies[text.charAt(i)-'A']++;
        }

        return frequencies;
    }

    public static double indexOfCoincidence(int[] frequencies, int n){
        double indexOfCoincidence =0.0;
        double lower=n*(n-1);
        for(int i=0;i<frequencies.length;i++){
            double upper = frequencies[i]*(frequencies[i]-1);
            indexOfCoincidence += upper/lower;
        }
        return indexOfCoincidence;
    }