String Permutation and Combinarion

StringPermutationCombination

    public static void generatePermutation(String str, final int index, final String prefix, List<String> list,
                                                   final char[] allChars, final char replaceAbleChar){
        if(str.equals("")){
            list.add(prefix);
        }else{
            char[] array = str.toCharArray();
            if(array[index]!=replaceAbleChar){
                generatePermutation(str.substring(index+1),0,prefix+array[index],list,allChars,replaceAbleChar);
            }else{

                for(char ch:allChars){
                    generatePermutation(str.substring(index+1),0,prefix+ch,list,allChars,replaceAbleChar);
                }
            }
        }
    }

    public static List<String> generatePermutation(String str,
                                           char[] allChars, char replaceAbleChar){

        List<String> list = new ArrayList<>();
        generatePermutation(str, 0,"", list, allChars, replaceAbleChar);
        return list;

    }