HashMap<String,Integer> map = new HashMap<String,Integer>();
    for(int i=0;i<bank.length;i++)
    {
        map.put(bank[i],i);

    }

    int len = start.length();
    int le=0;

    Character[] choices={'A','C','T','G' };
    char[] temp;

    Queue<String> Q = new LinkedList<String>();
    Queue<Integer> level = new LinkedList<Integer>();

    Q.add(start);
    level.add(le);

    while(!Q.isEmpty())
    {
        String test1=Q.remove();
        String test2=test1;
         le=level.remove();

         if(test1.equals(end))
                {

                    return le;
                }

      le++;

        for(int j=0;j<len;j++)
        {
            for(Character c:choices)

            {
                if(c==(test1.charAt(j)))
                {
                    continue;

                }
                else
                {

                       temp=test1.toCharArray();
                       temp[j]=c;
                       test1=new String(temp);


                    if(map.containsKey(test1))

                    {
                    System.out.println(test1);

                    Q.add(test1);
                    level.add(le);

                }


                }


       }



             test1=test2;
        }

    }

}